Sex Workers (or Anything Overtly Sexual)
We probably don't have to go into too much detail here, but there may be some gotchas you haven't considered. If your teen comes to you with an idea for dressing up like a witch, don't assume she'll appear in a shapeless black shift with a wart on her nose. Female-based characters can be reinvented with more sex appeal than you may think is appropriate, and a sexy witch can easily show too much skin for a youngster, tween or teen. Look at Elvira. Get the specifics before you give the OK.