Abby was first introduced in the Season 3 episode, Building 26. She attended a meeting of Nathan Petrelli and The Hunters', at which she told Nathan that she was going to shut his operation down due to the fact that he had kept prisoners without Miranda rights. Abby was later taken to see a captive, Tracy Strauss upon which she identified the blonde as such and inquired as to why she was being kept under heat lamps. Still not buying into the whole idea of humans having powers, Abby left with a promise to return with the proper documentation to shut the project down.
Later, Abby did indeed return with the papers stating that Nathan's project was shut down, but after a freak accident involving Tracy escaping and killing someone with her icy powers, Abby, a witness to the incident, agreed that the project was valid and needed to stay open.