A major aspect of the Harley Quinn cartoon has been redemption. After suffering years of toxic emotional abuse, Harley tried to heal, which led to her eventually joining the Bat Family. She's eager to atone for her sins, even the ones committed when she formed her own crew with Doctor Psycho and the rest. It's no easy feat, though, as Season 4 kicks off with Harley murdering Professor Pyg.
Source：https://www.cbr.com/harley-quinn-season-4-revives-joker/
