Honestly speaking I don't think she would want to live forever without her beloved Mister J. But, speaking of him, it could be his fault (most likely is) that she is the way she is. She was a trained psychiatrist after all (which is no easy thing to do) till she met him and was brainwashed, becoming as ditzy as she currently is.
I actually feel very sorry for Harley. She just seems to want to be accepted and loved. It is as if she has no self confidence and the crazy nature of the Joker (even though he is using her while accepting her) allows her to feel more at ease. Sad how people can be so easily manipulated. While it is only a comic, I believe that many people end up being like that in real life.
Honestly speaking, my memory of Street Fighter is a little hazy. I can recall the devious Bison, but Cammy White eludes me.