Ace and Harley have a similar bond with each other and that they were both used and abused by the Joker. In fact, it was Harley that revealed to her that the Joker kept the headband that brainwashed her into a docile vegetable while under Cadmus’s control. Afterwards, when she went to rebuild her Royal Flush Gang, Harley was there as well. She even gave her a chance for a new life, while saving hers from death. She admits to the girls that Harley is the closest thing she has to a big sister or mother, and looks up to her in strength.