I have done this and had it turn out well, and I have done it and had it turn out bad. Its really about getting to know the student. Is she just doing it to hang out with friends? Does she actually have interest in learning how to play something? Does she give any other teachers any problems with work ethic/attitude/etc?
See if its possible to have her come in on her own time and start learning how to read music and maybe even test on a few different instruments. If she has a good attitude and seems like she wants to learn, it could be a very good experience. Of course, this requires some extra effort on your part, or your assistant's part if you're lucky enough to have any, as you have to make sure the students isn't forgotten about after the fundamentals are taught.