That's true, I did lash out at her recently, before her diagnosis. She has been repeating over and over again the same mistake of breaking up and getting back with a man whom she both likes and doesn't like (who doesn't care about her in the least) and then complaining to me and other friends about it all. Finally I got fed up and told her not to mention him to me for at least a month -- this is when she got so insulted that she blocked my number and my email for 10 days before I contacted her semi-apologetically to stop that charade.

You say "over-empathy" - there's no such thing really. If you're aware of someone's feelings, you take special care not to hurt them or/and to help them. You don't immediately think of how that endangers you and how you should protect yourself from it. When you're emphatizing, it's not about you, it's about the other person. To me it looks like you don't understand the idea and are somewhat apprehensive of it; I think same applies to my friend. Ironically, she's in the medical profession. She non-stop talks about how she's constantly frustrated by her inconsiderate, annoying patients; I don't remember hearing her speak of them with sympathy.

Are you saying she should surround herself with people who are indifferent to her? Because those are the only ones who won't be trying to "fix" her.