I can only speak from personal experience, but when I was the girl in this situation, I just wanted to be left alone for a while and to have that need for space understood. When this space was given to me, I was able to move on and become friends with the guy again...it may take a while, but in my opinion, a healthy friendship can't happen until she moves on from these feelings.

Also, while she is moving on, if you start dating someone else, for goodness sakes don't rub it in her face. I'm not saying don't date until she's over you—that's not realistic—just if you can help it, try to not let her know that you're dating someone else. Maybe that's not realistic either...