Gia arrived in Port Charles in July 2000. While at a rave, she saw Emily leave and go to a hotel with an older man (an undercover cop). Under the impression that Emily was using drugs and knowing that Emily was a Quartermaine and a "rich girl," Gia started blackmailing her. This didn't sit well with Emily's friends. When the truth came out that Emily was not using drugs, Gia learned about the undercover cop and the murder mystery. She reluctantly started to work with the other teens to try to catch Zander, the suspected murderer.
After working closely to solve the murder mystery, Nikolas and Gia formed somewhat of a friendship. When she needed a place to live, he let her move into the extra room in his cottage, rent-free. When Gia' mom, who was already unhappy about Gia dropping out of college, found out about Gia's new living arrangements, she demanded that Gia move in with her. But Gia remained firm on staying with Nikolas. She even got a job as a PR assistant for A.J.'s football team to try to pay her own way. Little by little, the attraction between Gia and Nikolas became too big to ignore. The two made love and started dating, in that order.
Gia wanted to be the new Face of Deception, a signature model for the cosmetic company owned by Laura Spencer. Gia was up against her rival Elizabeth Webber for the part and played dirty to insure that Elizabeth wouldn't be chosen. Laura wanted Liz to be the model, but Laura's partner Carly was positive that Gia was the better choice. Behind Laura's back, Carly arranged for Gia to do a photo shoot with Lucky. On the night Laura was going to announce Liz as the new Face, Carly had Gia lock Laura on the roof of General Hospital to stop her. After realizing that Liz didn't want the job anyway and seeing the amazing pictures of Gia, Laura named Gia as the new Face of Deception.
Gia's blissful life came to a halt a few months later when Nikolas dumped her. What Gia did not know was that this move was part of a scam to protect Lucky and to find out once and for all what Helena was up to. Nikolas remained very much in love with Gia but he pretended that he wanted Elizabeth instead to please Helena. A heartbroken Gia tried to move on with her life by dating Lucien Cane, a rich handsome businessman, who Lucky detested for unknown reasons. Lucky and Gia also formed a bit of a friendship, and they even shared a kiss after Helena erased his memories of love for Elizabeth. Gia figured out that Helena was behind Lucky's sudden loss of love for Elizabeth and decided to help him. She distracted Helena to help Elizabeth steal the Ice Princess, the key to Lucky's programming.
Gia's hopes for a reunion with Nikolas grew when they shared a passionate kiss on the docks, but he quickly resumed his act and cast her off afterwards. So she attempted to make him jealous by arranging a date with Lucien in front of him. Lucien tried to take Gia to bed after their date, but Gia wasn't ready since she still loved Nikolas. She decided that Nikolas needed to get away from the Cassadines and tried to get Liz to help her. But when Liz refused, Gia realized that Liz and Nikolas weren't in love. She went to confront Nikolas and overheard Helena tell him to kill Elizabeth. Freaked out, Gia tried to warn Elizabeth and even attempted to protect her from Nikolas. When neither Lucky nor the cops would help her, she went to try to stop Nikolas herself. But she was too late; she found Nikolas with a "dead" Elizabeth. As Gia was threatening to call the police and telling Nikolas what a horrible person he was, Elizabeth woke up. Nikolas then filled Gia in on the plan and Gia forced Nikolas to let her help him. They reconciled and made love. He told her about meeting his father and she comforted him. Later she found a picture of Nikolas with his father and realized that Lucien was Stavros. Before she could warn Nikolas, Lucien showed up and took her to the room he'd decorated for Laura. He thanked her for her insight into Nikolas, but ended up locking her in a room with Nikolas when he showed up with Laura. Stavros and Helena were soon defeated and Gia and Nikolas made it out of Helena's underground maze without getting hurt.
Then Gia and Nikolas got engaged. They moved in together at Wyndemere and Gia devoted most of her time trying to convince Nikolas that he wasn't going to turn into his father. She even gave up her modeling career for him. After completing the shoot for her final layout as the Face of Deception, Gia celebrated with a glass of champagne at the Port Charles Grill. On the way home with Liz, she ran a red light and plowed into a car driven by Courtney Matthews, Sonny's newfound sister. Nikolas worked overtime to make it appear that Courtney was the one who ran the red light, not Gia. Even though Gia knew that she was at fault and not Courtney, Nikolas wouldn't let her take the blame. He paid off a witness to lie to the police that she saw Courtney run the red light not Gia. When Helena managed to escape from custody, she hid out at Wyndemere and blackmailed Gia into getting her money to go on the run with. Nikolas found out, but let Helena go in order to protect Gia and his involvement in the cover up of the accident. However, Elizabeth recovered from the accident and eventually remembered what really happened despite Nikolas' efforts to keep her distracted and in the dark. Elizabeth told them off for lying to her and making her lie to the police. But Gia didn't end up going to jail. Instead, Courtney surprisingly called a truce and enlisted her help in finding out if the Quartermaines, especially A.J., were lying to her.
Taggert was disappointed in Gia for letting Nikolas cover up her involvement in the accident and hired a private investigator to dig up evidence against Nikolas. Through the PI, Taggert got a tape of Nikolas confessing to his involvement in the cover up. As Taggert threatened to turn the tape in as evidence if Gia didn't leave Nikolas, Nikolas and Gia tried to cover their tracks. Ultimately, Gia told Taggert that she wouldn't leave Nikolas and the issue was dropped.
About this time, Nikolas realized how unhappy Gia was and how she yearned for the spotlight again. So Nikolas used his fortune to make Gia famous again by getting her on magazine covers. Gia had a hard time working with a "hands-on" photographer for one shoot so Lucky stepped in to save the day, making Nikolas jealous. Tired of their bickering, Gia decided to try to bridge the gap between the brothers. She urged Lucky to reach out to Nikolas as he grieved for his Aunt Kristina. Soon after, Lucky enlisted Nikolas' help when he discovered Rick Webber dead in the Jones' attic. Afraid that Luke was responsible, Lucky and Nikolas put Rick's body in a car and pushed it off a cliff to make it look like an accident. Gia then called the police as an anonymous witness. Scott caught on immediately and jailed Lucky, but let Gia and Nikolas off the hook. Later, Gia and Nikolas stole a key to a locker from Rick's stuff and discovered a human skull in the locker. They turned it over to Alexis who used it to get Scott to let Lucky out of jail.
Although Gia was not happy that Nikolas financed her return to modeling, she gave it up in the end in favor of working as a legal assistant for Alexis. She also worked with Nikolas and Ned in organizing Alexis' campaign for District Attorney. In her enthusiasm, Gia challenged Scott, the opponent, to a public debate with Alexis. Later, she explained to an upset Alexis that Scott obviously had something up his sleeve and that she bought them time to figure out what it was. Although Nikolas and Lucky got caught searching Scott's office, Gia and Nikolas eventually got their hands on the tape of Laura confessing to Rick's murder. They turned it over to Alexis, who took it to Scott and threatened to release it to the press. The tape never got released thanks to some maneuvering by Scott.
As Alexis became increasingly distracted by her daughter and the Alcazar murder trial, Gia began to cover for Alexis more and more. This meant less time with Nikolas, and he voiced his displeasure to her. He wasn't too happy either when she got herself into trouble for pretending to be a lawyer in Alexis' absence. Alexis forgave her for that one, but Nikolas and Gia began to grow further apart. She had been neglecting their wedding plans and Nikolas wanted to ask Gia to elope, but she stopped him with the news that she was returning to law school. When Alexis was representing Brenda in the murder trial, Gia got a little overzealous and pretended to be an assistant to the DA in order to secretly tape an interview with a protected witness. Her brother found out about the tape and demanded that she give it to him. Alexis wasn't too happy with her but didn't fire her.
Shortly afterwards, Gia and Nik's relationship began to really unravel when Gia started taking an interest in Zander's life. Zander had repeatedly gotten into trouble with drugs and the cops and Gia was trying to convince him to turn his life around. They also grew closer as Zander shared some secrets of his past with her. Nikolas was extremely jealous of the time Gia spent with Zander and he even tried to pay Zander to leave town. When Gia found out about this, she told him that she was tired of him trying to control her life. They broke off their engagement.
Gia began to focus more on Zander after that and they became quite good friends. They teamed up with Cameron to help Alexis during her trial for the murder of Alcazar. Gia even obtained an internship with Scott to try to get dirt on how he was going to prosecute Alexis. But Gia's hopes for a deeper relationship with Zander were thwarted when Emily returned to Port Charles. Emily played yo-yo with Zander's heart for awhile before ultimately pushing him away and moving on to Nikolas. Gia and Zander then started to become more than friends. Eventually Gia found out that the real reason Emily pushed Zander away was because she had breast cancer and didn't want him to have to watch her suffer and die. Gia confronted Emily and Emily begged her to be with Zander to keep his mind off of Emily. Since Gia had feelings for Zander, she agreed. But Gia got mad when Emily later told her that she felt jealous of Gia's relationship with Zander. Gia was devastated when she saw Emily finally tell Zander the truth. But Gia discovered that Emily also has feelings for Nikolas and when Zander discovered this as well, he fell into bed with Gia. Afterwards, Gia told him that it was a mistake since he still was obviously in love with Emily. She finally let him go and even helped him get dressed for his hospital wedding ceremony with Emily. When Zander and Emily appeared to be headed for splitsville only weeks later, she urged Zander to keep fighting for his marriage. After the Nikolas/Emily/Zander ordeal, Gia faded into the background.