Gina was a Six that had infiltrated the crew of the Pegasus. After she committed an act of sabotage, she was discovered to be a Cylon. Admiral Cain allowed her to be tortured and abused. When Baltar visited her, she was ready to die. Baltar attempted to emotionally connect with her and ended up helping her escape. The first thing that Gina then did was fatally shoot Admiral Cain.
Gina then managed to infiltrate the fleet's peace movement. In a show of good faith to convince Gina and the peace movement to halt their violence, Baltar gave Gina his nuclear warhead.
She and Baltar finally consummated their relationship after he won the Presidential election. She then listened to Baltar be inaugurated as President after which she set off the nuclear warhead, killing herself, destroyed Cloud Nine and some other ships of the fleet.
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