Liz Lemler, played by Anna Chlumsky, is alluded to in the episode "Up All Night".
Liz receives flowers from an anonymous person in her office. They were sent by Floyd, a lawyer working at 30 Rock. In "The Fighting Irish" we learn that Liz Lemler was Floyd's girlfriend, who worked as an accountant for TGS with Tracy Jordan and the flowers were meant for her.
In an effort to get together with Floyd, Liz Lemon fired her. An upset Jack Donaghy gave Lemler a promotion, moving her to GE headquarters in Connecticut and eventually leading to her breakup with Floyd, clearing the path for Liz Lemon.