What should i do?

I have a homeroom, where you cant be sure who your true friends are. Basically, because, they're the scholastic misfits, who are disrespectful to teachers and peers, and they get in trouble almost everyday. I have a couple good friends in my homeroom, but one of my friends was starting to act just like everyone else. She started lying, and when i caught her, she said it wasnt a big deal. Then she wanted to copy my homework, for the hundreth time. I said "No, just do it yourself" because i was tired of her just slacking off. She said, "well, I thought we were friends." And i said, " If you were really my friend, you wouldn't care, and if you are just my friend to take advantage of me, you're not worth it." and she said, " Thats just part of the reason im friends with you." I'm really sick of her just taking advantage of me, and she really doesnt have that many other friends. What should i do?