I am not too familiar with the Harley Quinn character as I have never read any of the comics or seen any of the movies. But my idea would be instead of having a superhero character who saves people, to have an evil woman character who just murders or tortures people each episode. She would live a normal live where she has a regular day job like a lawyer, therapist or something like it, and then her evil persona
It has probably been done before I imagine, but it would be cool I think. I just want to see evil murderous and sadistic women