Having been accused of cheating on a test because someone overheard a joke* between me and a friend, I have to offer this. Prove yourself to the teachers, and you won't ever have to worry about what Lucy says again. Don't worry about her, or what she says, or what she does, or who she talks to, or who does her bidding. Just make an effort on the homework, and wait till you get home to do the backwards work. And realize that high school is nowhere near equivalent to the real world.
* Friend and I had gotten the same score on the chem test, and we were teasing each other about who "copied" who. We ended up having to take the test sheets back to the teacher to show that we got different ones wrong. He actually hired me to work in his office part time after that, so we must have convinced him it was just a bad joke.