you have already tried several times; it seems you have been so subtle that she did not recognize that you were looking for her to change something.
Have you taken her class yourself or did you respond to the comments by participants? If the latter, I would strongly urge you to have a personal experience so that you can be more specific.
Does your instructor have access to a music library to choose from? Is it possible that it may be a matter of finances to purchase the music to use in classes? Could your help her with structuring a playlist?
On the other hand, classes that are boring and not motivating are usually very poorly attended. Can you possibly get another instructor to teach some of those classes to encourage a competitive spirit?
Giving feedback on things that need to improve is always very difficult. It is much easier to pat somebody on the back and saying “good job”.