how do mend a broken heart?

Nothing like ice cream or cookie dough! Time will help things to ease. She needs a friend to support her. Recognize his problems and hopefully she will be eventually glad it ended. It is truly ended now. She probably didn't see it coming, it was though. If possible, slowly get her out and about. Shopping might help. It is ok to grieve over a final ending, worth going through though. Good luck helping your friend.