Our 13-year-old wants to get her belly button pierced. I really wouldn't have a problem with it except for the inconvenience it might cause her while performing. I imagine the dancing, wardrobe changes, etc. would result in a lot of irritation/possible infection.
DD's idol is Sierra Boggess, and Sierra wears a belly button ring on Broadway.
I will happily field any personal stories and anecdotal comments about what it's like to be an actor with a pierced belly.
Instead of a ring, suggest she get a stud. It looks cuter (which is after all, the whole pount) and pressed flat against her tummy won't catch on anything. Lots of athletes have them and as far as I know, doesn't cause any problems due to physical movement.