I know it's hard to resist letting her have it when she pisses you off, but she's at that weird age between child and teenager, and she probably can't see any point of view besides her own. As time goes by the gap in age will seem smaller as you have more things in common.
For now, try talking to her like you would a friend, rather than a sister or child. Also, get a lock on your door.
also, and i'm not exactly recommending this, but whenever my sister would take something of mine i'd take something small of hers and hide it, ha.
Don't burn your bridges with her, as you might well be able to be friends with her in a few years, when she's feeling more stable, too.
Has your sister agreed to be nicer to you? I think she should be asked to, simply to point out to her that she's being quite unfair to you right now.
It might be that, at the moment, she feels it's unfair that her big sister has a disorder and that she's forced into close contact with you - insensitive, but I don't think you can expect that much maturity from her for now.
and when she borrows ur cloths just take somthing of hers without asking ( somthings she likes ) she will eventually catch on..
with the bathroom thing... uhh Knock on door??