Gia Goodman is the daughter of the influential Neptune citizen and professional baseball team owner Woody Goodman, who later becomes mayor. Gia has a somewhat ditzy and quirky personality. She tends to tell people exactly what is on her mind, even when they are sick of listening to her.
Gia started attending Neptune High during Veronica's senior year after transferring from a private boarding school. In Normal Is The Watchword, shortly after her transfer, she attended the class field trip to Shark Field and met Dick Casablancas, his brother Cassidy, Duncan Kane, and Veronica for the first time. She rode the bus on the way to the stadium, but was offered a ride in Dick Casablancas' limo on the way back when he saw an opportunity to make a new "friend." Whatever Dick's intentions, this probably saved her life as the bus crashed off a cliff just a few minutes later.
In Rat Saw God, on election night, Gia is at one of Dick's parties talking to Dick about how his father fled the country. When Veronica shows up looking for Duncan, Gia apologizes about how Keith didn't win the sheriff election and Veronica congratulates her for her father winning the Balboa County supervisor position. Gia also tells her about being interested in Dick. Gia also sees it when Deputy Sacks comes in to take Logan Echolls in for questioning.
In Nobody Puts Baby In A Corner, Gia is seen in Future Business Leaders of America. Later, in health class, Gia and Veronica pair up for an exercise involving telling your partner that you have an STD. Gia mistakenly thinks that chlamydia is a flower. Gia saw a chance to become better friends with Veronica when she invited Veronica to her slumber party. Veronica had an ulterior motive during the slumber party though as she was investigating families that Meg Manning had babysat for and Meg had babysat Rodney Goodman while Gia was away at school.
In Look Who's Stalking, Gia turns to Veronica for help when she receives a mysterious DVD in the mail containing camcorder footage of Gia at her brother's soccer game. Gia hires Veronica to find out who sent her the creepy footage. Gia and Veronica's friendship turns heated when a feud erupts between Woody Goodman and Keith Mars. Gia kicks Veronica off the case, but Veronica still rushes to Gia's aid when she realizes that Gia's stalker was Neptune High janitor Tommy "Lucky" Dohanic and that he was still inside the school with Gia. Lucky is arrested, but he is let go when the Mannings pay for his bail. Later, at Logan's Alterna-Prom, Gia thanks Veronica for saving her and apologizes for the bad things she said about Keith.
In Happy Go Lucky, Gia comes to school and gives Veronica cupcakes as a thank-you gift. Veronica thanks her and tells her that she needs to study, but Gia thinks that Veronica is mad at her because of what happened between their fathers. Veronica assures her of the opposite and Gia suggests that they study for their health final together at Gia's house. Veronica agrees and Gia happily walks off. When Lucky comes into lunch area shooting a gun, Gia stares at him shocked and Veronica quickly makes her crouch behind a table with her. Lucky is shot and killed by school security and no harm comes to Gia. Later that night, Gia and Veronica are studying at the Goodman house and Gia is unaware that Veronica is using the opportunity to copy her father's hard drive files.
In the film, it is revealed Gia was on a boat with Susan Knight, Carrie Bishop, Luke Haldeman, Dick Casablancas, and Stu "Cobb" Cobbler a year after Veronica left Neptune when Susan overdosed on a drug provided by Cobb. Gia, Luke, and Carrie drop the body into the ocean (Dick was too drunk to have been aware) and made up a story of her falling overboard while drunk, but Cobb photographs them in action, thus blackmailing them into doing his every bidding, such as having Gia as a girlfriend (while Gia is engaged to Luke). When Carrie (as Bonnie DeVille) is ready to reveal what really happened, Cobb forces the group to help kill Carrie. However, Gia picks up Carrie's hacked Galaxy Tablet (provided by Vinnie Van Lowe) and is thus filmed texting Logan, tricking him into showing up at Carrie's place and thus being framed for murder.
When Veronica confronts Gia about this, she confesses to the entire thing, unaware that Cobb is listening in on a nearby radio station due to Veronica's malfunctioning bug. She approaches the window when she tells Veronica how she wasn't allowed to have curtains and how Cobb might be watching them that very second. She waves and before she could tell Veronica to try and act natural, Cobb shoots her in the stomach before aiming for Veronica. Gia lies mortally wounded on the floor as Veronica calls the police, and stops breathing as Veronica assures her that help is coming.