Harley was very compelling in batman animated and at the start of her comic introduction she still had the elements from dcau that made her a fan favourite (she was cute and quirky but also was a wild card) but nothing pure and good can last in comics so eventually she became a watered down version of who she used to be and got over saturated everywhere. That being said harley is an example of a female character overcoming years of domestic abuse and coming out alive and hating her abuser so i can understand the appeal
I hate that Harley was supposed to be intelligent but she let The Joker play her as a fool. I feel sad for her, she should've known better than to be played like that and have her life ruined. On the other hand there was probably a deep-down subconsciousness to her that wanted to be released and The Joker's attention toward her was the excuse to give-in to what was always there deep down.
With all that said , the character is okay in small doses.