I used to have someone just like this at my old school!! Try to tell an adult, but if they don't do something, then you can start reacting. DO NOT ignore her, for starters. If you do, she will think that you're a punching bag. She'll continue to torment you. Just say that she's jealous that you're happier and more successful than her. Also, any time you can, be around a large group of your friends. It can intimidate her, or your friends can back you up if it doesn't. Also, if you say something, and she physically hurts you, do NOT hesitate to beat the living sh-- out of her. I don't care what your parents, teachers, friends, etc. say. If she hurts you, you have all the right to defend yourself. But, never be the one to throw the first punch. If you get in trouble after she hurts you, and you defend yourself, say "It's self-defense. Shouldn't we stand up for ourselves?" And, finally, here's a tip: Don't roast her. Be kind to her. Even if you don't mean it. If she's harassing you, just go off-topic. Say something like "I love your hair!" or "Your shoes are really nice!" or something along those lines. Don't be mean, she will snitch, and you will end up getting in trouble. I have experience with people like her. Trust me, fighting back with insults NEVER works.