Yes, I agree with you that it’s foolish of her to say this, whether she means it or not. The words we speak will determine the course of our lives. There’s a saying that goes like this: If you want to find out where you will be in twenty years, then just listen to what you’re talking about now. In the book of James in the Bible you can read how important the tongue is (James 3:1–12).
We recommend that you talk to her. One way you could do this is by saying that you believe that there is an invisible world which has angels and demons, and that you think it’s a bad idea to get involved with the evil powers there. Your teacher should also be involved, so that no-one in the class is given bad nicknames.
Good luck with your talk!