That kind of killed the movie for me, she is the daughter of your friend, goddamit, romantic interest is not the only way to have a deeper relationship between unrelated persons of different sex.

That doesn't make it good. Everyone hated it then, nobody wants it now. It trivializes Batman's relationships with everyone and completely ruins TKJ. I didn't think it was possible for DC to ruin The Killing Joke, but goddammit they found a way.