Catwoman has only ever murdered one person in her whole life: the crime lord who had gleefully tortured her brother-in-law to death and her sister to insanity (his reason: because Selina loved them and he loved hurting Selina). And even then, she only killed him because he outright told her that he would come after her loved ones again.

Sure, Selina is a criminal, she killed one guy and she steals from rich people. But she is nowehere near the level of Poison Ivy and Harley, they are in a whole different league.