When she found out she was sleeping with the Joker, I couldn't help but think about that scene in "JD's Revenge", when that sister first found out she had been really sleeping with JD, a violent gangster who was murdered years ago, who came back and slowing but surely began possessing the law student she was having an affair with behind her husband back. Her husband walked in on them one evening screwing in the bedroom, right when the law student got fully possessed by JD's demonic spirit. When her husband went after him, he whupped her husband ass, and came but so close to slitting his throat. When he let her husband live, and left, his wife still had this look on her face like a confused cat...lol. You couldn't tell if she was shocked or still smiling from the sex.
None of this happened in this movie, but it reminded me of what can happen when sisters jump in bed with anything. In fact, the Joker was crazier than JD, and he wasn't even possessed.