I have to agree with you on not being the biggest Harley fan. I'm actually kind of interested in the new take from The Caped Crusader Amazon show where she uses psychology to manipulate her victims.
What’s great about comics is there are multiple jumping on points throughout the years. With Marvel and DC you can find one of those places to jump onto and just start with your favorite character or one that interests you. But there’s other awesome indie titles as well! You can always get collected editions too so you can read a full story in one book instead of trying to find all of the single issues separately.