Is it wrong for my mum to go on my facebook and try to look at everything I do?

I'm a fifteen year old girl who has a facebook account - just about like every other teenager in the world. But my mum insists on going on it, actually logging onto my actual account to look at everything I do, read my conversations, my messages and my wall posts. We've argued about it before, I've told it's wrong, that I don't like it and she shouldn't do it because first, I already tell her everything and there's no need for her to look at it. I've tried explaining that it's my personal social life and that anything she should know I already tell her. Then she says that there shouldn't be anything I don't want to show her. It's pissing me off so much, and I can't tell me friends because they'd just be like 'WTF, you're mum is a freak'. She is trying to blackmail me with this, by saying if I don't let her see my facebook than she won't let me go out or invite friends over. WHAT SHOULD I DO?