I agree about the boundaries. So much easier said than done, though...

I find that the phrase "what can I do?" can be more liberating than it sounds. There IS only so much you can do. She knows that. And perhaps if you involve another (your wife, a professional) in your communication with her, then the risk of you being manipulated is much lower.

If you are able to just outright say that you prefer she not get in touch with you (both to yourself and her) then it's the best thing to do.