I know this is very extreme in that it would take effort, but you might want to consider a white list approach instead of your black list approach.

when you have a black list approach, you basically trust everybody except for a small number of people whom you block.

when you have a white list approach, you basically trust almost nobody except for some people whom you allow to post on your wall.

I am sure FB would support both approaches. It is just that while you are using the black list approach, you are vulnerable to her tactics. What if she opens a new FB account under a different name and posts vicious things about you AGAIN? And you will need to block her new account - and she might open yet another one?

Surely it would be a pain to have a whitelist, but at least you will get to sleep well...