She copies my homework! What should I do!?!?

Okay, here's the thing, I'm 11. (grade 6) xD ....and there's this girl who doesn't really do her homework, actually she doesn't even do her homework at all! Last year I was in the same class with her and I always saw her do her homework in the morning or sometimes she copies homework off her classmates. But this year she copies my homework, urgh! She's a tomboy and really tough and she thinks she's so grown up. I feel like slapping her..She likes to bully timid and shy people in my class cause' she thinks they are weak against her. Anyway, there was one time when it was recess and we two were the ones left in class cause I wanted to get ready for the next lesson after recess. She asked me to hand my homework to copy and I said no. I walked out of the classroom, (by the way, the class monitor is supposed to lock the door but she forgot to bring her key) and the next thing I knew she reached for my bag and took my homework out and started copying it! At class, the teacher praised her for doing her homework and decided to boost her "homework" marks. I was so angry and I wanted to tell the teacher that THOSE ANSWERS WERE MINE! I'm not gonna let her have a sweet life and me being her servant. NOT IN A MILLION YEARS I WOULD LET HER COPY MY HOMEWORK!!!!!!! (sorrry, I'm quite sensitive about my classwork and homework because I work really hard to do them..) What should I do if she corners me with her friends and forces me to let her copy my homework? If I tell the teacher she will bully me for sure...so, my dear yahoo.com friends, please help me!