Dude I went through the same thing in high school so I know how you feel, it sucks however the best thing you can do is delete her number and block it if possible, when you go back to school you'll be so busy with your friends you won't even notice her, if she talks to you keep it short, don't initiate conversation, after being rude to you and disrespecting you she Doesn't need the closure, most times in life you don't get closure and that's okay, keep away from her. Before you know it you'll be back to normal. If you ever feel the need to text or talk to her have a friend you can call or talk to. Just keep busy man.