I'm so sorry you're in this horrible situation. I've been bullied and I understand the feelings of powerlessness, injustice, anger and frustration, as well as the betrayal of other people doing nothing or even actually supporting the bully.

I agree with others that therapy is often the most helpful thing, especially if you're vulnerable because you're not ready to move out yet.

What do you think you can do in the situation now? Can you get a lock put on your bedroom door (one your sister can't break) and lock your things in there when she comes round? Can you leave the house while she's there?

There's a website it might help to read, to know you're not alone and it's not your fault. It also has links to other resources:
http://www.bullyonline.org/related/family.htm

I really think you need real life support, though. You shouldn't have to do this on your own. Do you know where to find about what therapy's available to you?