I had this happen to me before. I found the strength to block the "friend's" emails and I never added her on facebook but I would have found a way to block her there too.

Without sounding too insensitive, but I am gonna be straight up frank with you. YOU doing this to yourself. You are reading her emails and not blocking her to upset yourself and get yourself annoyed and there is no reason to do this anymore. Stand up to yourself and your curiosity.