In Harley Quinn Season 4, Harley is faced with her biggest emotional crisis yet. Physically, she's firing on all cylinders and feeling anxious to stop crimes with the Bat-family. Unfortunately, Harley isn't mentally ready to make the jump into her new career officially. She just doesn't understand Batman's no-kill policy, plus her character is clashing with Nightwing's personality.
Source：https://www.cbr.com/harley-quinn-season4-losing-support-system/
