What should I do about my sister?

I've got one (sister) just like that! They think they are better than anyone else and especially a family member. They act like this around their sisters because they are infact insecure and self centred. Give her space and let her get on with going right up her own bum. Something will happen to her to make her crash back down to earth and get a dose of reality. Let life do this for her. You just stand back and be there for her when it does.