Mariah grew up with her mother off and on, living in a dump in the Hawthorne District in Portland. Her mother, Helen, was an on-again, off-again, follower of the self-help organization known as The Path, which was run by Ian Ward. Tyler Michaelson referred to her mother as a nut job who was rarely around, and had been told that her father had abandoned them. Mariah said that Ian had been the closest thing to a family she ever had. Growing up in poverty, Mariah learned the only way out was to steal, and got in a lot of trouble.
During 2012, Mariah was engaged to Tyler Michaelson, and they were living in Los Angeles. But when Mariah cheated on Tyler, he broke off their engagement and moved to Genoa City where his sister Leslie had her law practice. Mariah continued to call and call, wanting Tyler to forgive her and reunite.
By 2013, after Tyler had blocked Mariah's calls, she discovered that Tyler had moved on with heiress Abby Newman. So Mariah moved to Genoa City. Tyler suggested to Abby that they move in together, and she agreed, as Mariah, (shown to viewers only as a tattooed arm), looked on. Tyler and Abby put an offer on a house, but lost it when the realtor received a call from someone claiming to be "Tyler's girlfriend", saying that they had changed their mind. Viewers saw the stalker with the tattoo watching them at Crimson Lights coffee shop.
Tyler and Abby looked at an apartment and decided they wanted it. Tyler left, and Abby was to return the key. After Abby failed to come home that night, Tyler found her locked in the apartment the next morning, getting in with the key which was still in the door. They found Abby's phone in the hallway where viewers had seen the tattooed woman smash it. Abby said she was certain that she had been locked in by Mariah, and walked out mad after finding Mariah's number back in Tyler's phone. Tyler texted Mariah, telling her to get the hell out of his life. Viewers saw the tattooed woman receive the text. Later when Tyler was about to delete her number, Abby grabbed the phone, called Mariah, and left a voice mail that she wanted to meet with her. Abby later set up a lunch meeting for the three of them, but Mariah did not show up. Afterward, a relieved Tyler called Mariah and said he was on his way over.
In 2014, Sharon Newman began having hallucinations of her dead daughter Cassie. They were so real, that Sharon could reach out and touch her. Thinking that she was going insane, Sharon underwent electro-convulsive therapy which wiped out a lot of her memories. But when Sharon's ex-husband Nick ran into an older Cassie lookalike named Mariah, he got her to admit that his father Victor Newman had been paying her to gaslight Sharon. Victor had hoped that Mariah could drive a wedge between Sharon and Nick who had reunited after many years, and that she could find out the secret that Sharon had was keeping from Nick. Victor had paid Mariah more than a year's worth of her usual waitress salary, and once it was exposed, Mariah begged Victor to let her get close to Sharon and still find out the secret for more money. Victor said no, and threatened Mariah that if she did not leave town, he would notify the authorities in Portland where there was a warrant for her arrest.
Mariah went to see Sharon and apologized for hurting her, telling her that she actually liked seeing Sharon and Nick together, and hoped they would reunite. Later Mariah made a phone call telling someone that she was in trouble and needed help. Ian Ward, the leader of the New World Cult which she had left, showed up at her door. Ian was quite familiar with Victor Newman, and even more so with his wife Nikki, who had been a member of his cult when she was in her teens. Ian reassured Mariah that he would handle Victor.
After Tyler and Abby's engagement party, they decided to take a room which happened to be at the same motel where Mariah was staying. Outside their room, Abby ran into a person who looked just like her dead niece, Cassie. Having just found out that Victor had paid a lookalike to torment Sharon, Abby lit into her. But Abby was shocked when Tyler came out of the room and joined them, calling the young woman Mariah. Once Abby realized who she was, Abby let Tyler know that his former fiancé had been paid to drive her half-brother Nick's wife insane. Abby left, but Mariah followed Tyler back into his room. Mariah planted a kiss on Tyler, telling him that he was just the pet of a bored heiress, and proclaimed her love for him. Tyler accused Mariah of always only thinking of herself, just like when she had cheated on him with his boss, and told her to go back to L.A. Mariah said that she still had business in Genoa City, and Tyler told her to stay away from Abby. Mariah purposely dropped her bracelet beside the bed to for Abby to find. Abby found it and promptly confronted Mariah, telling her that she was going to get Mariah arrested. Tyler had to break them up.
Later Abby and Tyler confronted Mariah, and Abby tried to pay her to leave town. Mariah tore up the check and refused. As Tyler left, Mariah warned him that she knew all his secrets, and later she pulled out a newspaper clipping with the headline "Portland West Hills Mansion Robbed. Culprits Still at Large".
Sharon visited Mariah, and ended up taking her grocery shopping. She questioned Mariah about her relatives, trying to come up with a logical reason for the resemblance to Cassie. Mariah claimed she had no family, but said that her deceased mother's name was Helen. When she returned, Mariah discovered that all her money had been stolen from her room. She called Ian for help, and they decided that accepting Sharon's friendship was her only option. Mariah later showed up at Sharon's asking for help after all her money had been stolen from her room. Sharon warned Mariah that she knew how she had been interfering with Abby and Tyler's relationship, but gave her some cash to tide her over.
When Mariah returned to her hotel room, she was arrested to be extradited back to Portland for breaking and entering, and burglary of art, coins and jewelry she had taken while the guy slept. When Tyler found out, he went to Portland to be a character witness for her. Mariah asked Tyler to get Sharon to help her. Tyler relayed the message, telling Sharon about her tough life growing up. Sharon related since she had grown up under similar conditions, went to Portland, got the charges dropped, and brought Mariah back to Genoa City. Sharon got Nick to begrudgingly give Mariah a job tending bar at his club, The Underground, and Sharon paid the rent at her apartment. Mariah informed them that it was only temporary, until she could pay Sharon back. Sharing her news with Ian, he advised Mariah to take advantage of Sharon, but Mariah said she did not want to push her luck. Nick asked Noah to return and train Mariah, but he was resentful of her and tested her by leaving his wallet on the bar. Mariah passed the test until Abby took it, emptied it, and stashed it in the ladies room, setting up Mariah. But when the police showed up, and Noah found out what Abby had done, he confessed all. Mariah got upset and quit. But Sharon convinced Nick to apologize and hire her back. Nick did, but made her agree to give up a portion of her paycheck until her debt to Sharon is paid, then to leave town. He also suggested she stop with the attitude which provoked people, and to make up with Noah.
Later Victor overheard Mariah telling Ian that their plan was not going to work, and Nick saw Ian leaving Mariah's apartment. Nick asked Mariah what her connection with Ian was, and she told how she had know him since she was a kid, and he was the only father she had ever known. Nick warned Mariah that Ian had gone to prison for fraud and had prayed on both his mother and his daughter. Sharon, Noah and Faith were preparing their first dinner as a family again when Mariah showed up to pay Sharon some of the money she owed her. Sharon invited her to stay for dinner, Mariah declined, but Sharon insisted. Dinner went well, and Mariah was getting along well with Faith, but Nick warned Mariah not to get too close to his family. Mariah accused Ian of playing her like everyone else. But Ian claimed that Nikki had made their relationship sordid and ugly, and misled him about Dylan's paternity. Ian suggested that Mariah get Sharon to let her live with them, so Mariah told Nick and Sharon that her room had been broken into again, and she was afraid. Sharon asked why she had not gone to Ian. Mariah said she had promised Nick that she would stay away from Ian. Sharon invited her to stay with them, and Nick surprisingly offered to help her get her things. Mariah declined his help, and returned to her room and Ian, telling Ian of her success.
Mariah tried to convince Nick that Ian was not an evil person, that he had helped a lot of people, and cared about her, taking her in and expecting nothing in return. Then Mariah suddenly started going after Nick, finding ways to be alone with him and to hug him, wearing skimpy clothing and cooking for him. Nick caught Mariah on her phone angrily refusing to give her mother money, and he reminded her that she had told Sharon that her mother was dead. Cassie told Nick how her mother never loved her, was never there for her when she needed her, so she was dead to her. When Nick asked, Mariah told him that her mother Helen was a nurse in Kentucky, last she heard. Mariah reported to Ian that she had heard from her mother, and Ian reacted with dread. Noticing Mariah's apparent attraction to Nick, Ian warned her that she had a good thing going there, and not to screw it up.
Mariah literally ran into Kevin Fisher at the coffee house. Exchanging barbs about each other's clumsiness, Kevin was shocked at how much she resembled Cassie Newman. Comparing their bad days, they agreed that both their lives were cursed, as they quoted from the book The Kingdom Beyond, remarking how they had both escaped reality as kids by reading it.
Mariah confided in Nick that her mother Helen had been a pediatric and obstetric nurse and an occasional a bartender, a free spirit drifting from job to job and in and out of Mariah's life. Nick caught Mariah on her phone angrily refusing to give her mother money, and he reminded her that she had told Sharon that her mother was dead. Cassie told Nick how her mother never loved her, was never there for her when she needed her, so she was dead to her. When Nick asked, Mariah told him that her mother Helen was a nurse in Kentucky, last she heard.
Intending to seduce Nick, Mariah came down the stairs wearing only a teddy announcing a surprise, and found only Sharon. Mariah tried to make excuses, but Sharon saw through her lies. Mariah swore that Nick wanted her, but Sharon told Mariah that Nick would never cheat on her to be with someone who looks like his daughter. Calling Mariah a thief, liar, and a tramp, she kicked Mariah out of the house, telling her to never return. Mariah tried to get help from Ian, but kept getting put off with text messages instead. Kevin bought a Harley motorcycle, and he and Mariah decided to disappear together on it, but Mariah never showed up. Instead she had found Ian to say goodbye, but he convinced her to run away with him instead. Stopping by his storage unit on the way, he gave Mariah a glass of wine that was drugged. Mariah woke up later confused and wearing a wedding gown. Ian told Mariah that their Paths were to marry, and Mariah realized he was as crazy as everyone had told her. But after giving her a drugged glass of water, Ian forced Mariah to sign the paperwork and marry him, which his old cohort Clarence officiated. Ian left them alone together, but Nick, Sharon, and Dylan showed up with the police and rescued her.
Later in the hospital, Nick and Sharon explained to Mariah how he had discovered that she had been born Cassie's twin and Sharon's daughter, but that she had been sold to Ian by Sharon's delivery nurse, Helen. Mariah finally believed it, but refused to forgive Sharon for kicking her out, and refused to become part of their family. Nick was able to assure Mariah that the marriage to Ian would be invalidated and talked her into staying in town at least. But Mariah approached Kevin again wanting to leave town, Kevin was no longer interested in going, but she made Kevin happy saying she needed him as a friend. Mariah told Noah that Sharon wants her perfect daughter back, but Mariah knew that she would never measure up.
Mariah witnessed Sharon dreaming, mumbling about her secret, saying, "I lied. I should have told Nick who her father really is." Mariah misinterpreted it to mean that Nick was not Faith's father and told Victor, expecting a reward that would allow her to leave town. Victor made her wait until he could get their DNA tested to be sure.
Although still belligerent toward Sharon, Mariah did give in and agree to be a bridesmaid for Nick and Sharon's wedding. She began to get closer to both Kevin and Summer's husband Austin, who both came from the wrong side of the tracks, and could relate to her not fitting in. Kevin and Mariah developed a fun rapport, and Mariah asked him to attend the wedding of Sharon and Nick with her. Mariah began to mellow toward Sharon, especially after Phyllis interrupted the wedding, and it was not completed as Sharon worried that Phyllis would expose her secret.
Kevin took Mariah to a hotel to keep her safe, but they returned to town when they heard that Ian was in jail. Victor returned and informed Mariah that she had been wrong, and the DNA test had proved that Faith was in fact Nick's son.
Nick made an appointment with the justice of the peace for Halloween to complete their wedding vows. Mariah had a change of heart after being reminded by Kevin that Sharon was the only one who had ever believed in her, and took Faith trick or treating after a happy family photo session. But again, the marriage did not happen due to Phyllis' revelation that Sharon had changed the paternity test results, and that Summer was truly Nick's daughter. Nick moved out, and Mariah was the only one who stayed and supported Sharon.