Hi,
I had a similar fb issue. And one day, after a vodka and coke at 1pm I just thought f-it! and I blocked or deleted or whatever you call it. It was theraputic. Facebook doesn't mean she is your friend. It is a form of communication media. And yes, it might feel like the last link that you have, but like you said it's all on her terms. If you can keep the fb friend and have it on your terms also- post on her wall- make comments (that her friends and family will see) then fine, it's balanced, but if you are keeping it in the hope that it will mean something to her then you are ignoring your needs- and that is what will send you crazy.
xx AMie