"she reads my diary, opens my post, lies to me, describes ways of killing him just to make me cry, doesn't like me reading which is my escape, complains when I try to talk to her, has a go when I don't, complains when I stay in my room, complains when I want to go out with my friends"
It's understandable that you feel annoyed that your privacy has been invaded, and about her complaining. What is this about her describing ways of killing him? Try to find some space for you to collect your thoughts about all this. And don't leave your diary where she'll find it.