She is a stunning blonde with an independent streak and a contentious relationship with Castle.
Season One
In the series premiere, "Flowers For Your Grave", she is introduced during the release party for Castle's concluding book of the Derrick Storm series, Storm Fall. Although she badgers Castle during the party about a how there are rumors that he hasn't written in months and that she needs the new manuscript, she is not seen often hassling Castle in person through most of the first and second season. Castle is portrayed as talking to Gina on the phone often, usually about missing a deadline or being late with a manuscript. Gina apparently works for Black Pawn, as the name of a publishing house.
Season Two
At the end of the second season, Castle brings Gina to the station to tell the detectives that he is spending the summer in The Hamptons with her. Gina indicates that she and Castle had recently reconnected, and they appear to be rekindling their previous relationship.
Season Three
When Castle first returns to the city in the fall, he appears to be still seeing Gina. She attempts to bond with Castle's daughter Alexis by buying her tickets for a Taylor Swift concert- her company having recently been approached to publish Swift's autobiography-, though he is initially upset over this. Gina reveals that this overly protective attitude towards Alexis was a major reason behind their divorce, and Castle admits that he was wrong and will try to correct his past mistakes.
As of her last mention on screen, she and Castle had resolved their argument and had a stable relationship. However, she was significantly not mentioned for several episodes after that, even in cases where Castle's relationship status has come up (e.g. why he chose not to sleep with Natalie Rhodes). Castle finally ended the relationship when he recognised that the two were no longer in love, admitting to Martha that he wanted a relationship with more magic in it.
Trivia
Gina was originally supposed to be a regular character on the show, even included in the first season's promotional photos with the rest of the cast, wherein Tamala Jones' character Lanie Parish was supposed to be the recurring character. By the time the show was picked up by ABC, Lanie had become a regular character and Gina had become a recurring character.[1]
Griffin?
There is some confusion to Gina's real surname. She was listed on ABC's press releases as Gina Cowel in "Flowers For Your Grave" and Gina Griffin in "Anatomy of a Murder". Gina Cowell is thanked in the acknowledgements for the published "Heat Wave" novel. And in the episode "Poof! You're Dead", her name is Gina Griffin on the newspaper article of her and Castle.
