I had a feeling this topic would turn into a bit of a shit show.

That said, showing Harley emancipated from the joker already doesn't have much impact when the Joker didn't really do anything that bad to her when she was Harley (Quinzell and Quinn are basically different people at this point), certainly nothing she wouldn't do to other people. (I'm not trying to say that leaving your girlfriend to drown in a car is a good thing to do, but when you're both psychotic murderers, it's not anything more than par for the course)

I think they need to show the bad for her leaving to have any impact, showing someone leave an obviously bad relationship is going to leave a far more profound message than her just having already left, you know?

It might be a bit controversial, but I think this moment from mad love would be a great cold opener for the film to just show that raw and terrible abuse Harley faces at the hands of the joker, it easily sets up Harley's motivations for leaving and makes her a far stronger character for getting out of a relationship like that.