Gina is a Humano-Cylon who was "rescued" by the Pegasus, claiming to be a survivng civilian dock worker. After befriending the crew, she betrayed them to the Cylons, whom summarily boarded the Pegasus and terminated 800 of her crew.
Gina was captured and tortured by the Pegasus crew. When the Pegasus encountered the Galactica fleet, she was turned over to Gaius Baltar who examined her, concluding that Cylons are susceptible to the same psychological afflictions as human beings (Pegasus).
A variant of Number Six, Gina is physically identical to her "sister" with the exception of having shorter, darker hair. Gina also has lost her Cylon faith, perhaps as a result of the Cylon attack on the Pegasus or her subsequent abuse at the hands of its crew.