Rebecca Flynt was a vampire during season one of Being Human.
Season 1
In the opening of There Goes the Neighborhood: Part 1, Rebecca Flynt (portrayed by actor Sarah Allen) decided to sleep with Aidan, after going out on a date with him. Rebecca had no idea that Aidan is a vampire and he was unable to control himself with her. After Rebecca dies, Aidan askes favor from Bishop to dispose of her. However, Bishop decided to turn Rebecca. As a result, she became a strong, powerful vampire that harbored a deep hatred for Aidan, but she desired to be with him. At first she had no compunction against killing and feeding on humans. However, her conscious grew, and she was able to see the pain in her victim's eyes, resulting in a change of heart. In Wouldn't It be Nice (If We Were All Human), Rebecca sought out Aidan to help her get over the desire to kill humans. However, she couldn't stand the taste of human blood from the blood bank (as opposed blood from live subjects), and she can't substain herself on vampire blood for long. Suffering from what looked like withdrawal symptoms similar to those of withdrawal from drug addiction in a human, Rebecca stated that she wasn't as strong as a human. She left Aidan, (presumably to go back to hunting humans for sustenance, despite her desire not to).
In It Takes Two To Make A Thing Go Wrong, it was made definite that Rebecca returned to killing humans for food. While serving as an agent for Bishop, Rebecca sent a DVD in a form of a pornographic snuff film, that includes Rebecca attacking an older human male to enticed Aidan back to the "family". Rebecca seemed to have re-embraced the vampire life - not out of a feeling of doing what
Rebecca after killing Marcus
comes naturally to a vampire, but because she felt she had no alternative.
In Children Shouldn't Play with Undead Things, Rebecca saw Aidan playing with Bernie and she talked to Aidan about their relationship. Rebecca also asked him if he was a father once, since he was being kind to Bernie.
In I Want You Back (From the Dead), Rebecca turned Bernie into a vampire so that She, Aidan, and Bernie can be a family. Moreover, turning the boy was the best thing Rebecca can get for a child. While she was happy with this, Aidan objected and he hid Bernie. In a motel, Rebecca ordered Bernie to drink hospital blood, but Bernie refused, which caused an argument between them. Aidan convinced Rebecca to stay, while he takes Bernie to get fresh food.
In Dog Eat Dog, Rebecca was warned about the Dutch, but she was not scared. When Aidan asked Rebecca for her help, she declined because Aidan killed Bernie.
In Going Dutch, Rebecca found out that Marcus killed Bernie's bullies, and he attempted to turn Rebecca to his side. However, it failed when Aidan was trying to rescue Heggeman and Marcus stood in their way. After Marcus attempted to kill Aidan, Rebecca killed Marcus and she helped Aidan save Heggeman. Rebecca told Aidan that Marcus was responsible for Bernie's death, and he killed Bernie's bullies. She then told Aidan to kill her, because she knew that she was supposed to die that night with Aidan, not live this life as a vampire. So, Aidan regretfully staked Rebecca, in her last moments she managed to tell him 'Thank You' before she crumbled away to dust.
Season 4
Rebecca reappears in the episode Rewind, Rewind... to Aidan and Josh to ask Aidan out on a date, while Sally watches on from a nearby bench. For Sally, knowing that Aidan will kill her, shows up on their date to break them up, to which Rebecca thinks Aidan has some disease and leaves, ultimately preventing her own death, and future vampirism.