Harley’s reaction to Diablo’s story in the bar is really interesting. She gets really passionate and angry when she’s telling him “You own that shit.” with regard to killing children. Now, the first text that pops up during her introduction sequence describes her as an “accomplice to the murder of Robin”. With this extra bit of information, it seems to me like her impassioned speech wasn’t so much directed at Diablo, but at herself. If that’s the case, she’s definitely having a hard time coping with her involvement in Jason’s murder. Maybe she’s not as far gone as she appears to be…
also to add to this: her dream sequence - what she desires the most - was a happy life with joker and TWO KIDS. and that coupled with the fact that in the scene where joker is surrounded by knives, there is also baby clothes laid out too. she could/would have been a mother but circumstances must have led to something happening to her kids. the dream sequence makes it really clear though: harley wants a family. she wants children. that’s what she desires the most. and perhaps the weight of killing/being complicit in the murder of a child is finally catching up to her.