You could say as long as she wants to pay for the class, that's fine. But the chairs are for paying students. I would ask why the friend is so skittish. A friend of mine would not go to classes unless I took them with her. I always paid and sat quietly with my friend. One time I had a teacher watch me work, then asked why I took the class, and I said there is always something to learn. Since I never wanted to be one of those people that try and tell the teacher an easier way to do whatever they were teaching I would do what they instructed. And I think I always did learn something new.