How often should a 15 yr old girl have her eyebrows waxed?

My granddaughter has become obsessed with having her eyebrows waxed (for no apparent reason). She has beautiful eyes & her eyebrows are not in the least bushy. She spends alot of time putting on & taking off make-up & last yr, she skipped lunch for a week at school so that she could have her nails done! It is really starting to worry me as she truly is a beautiful girl but is becoming so obsessed with her looks tthat I am growing concerned. She had her eyebrows done about 2 wks ago (against my knowledge & consent) & has already made an appt to have them waxed again this coming weekend! Please help me...If she sees that it is not normal to have your eyebrows waxed so often, maybe she will not think I am such an old fogey...I am her Grandmother & she has lived with me most of her life but I don't consider myself old-fashioned---altho i can do without rap! I do thank you so much for all of your help. (And prayers are appreciated, too...it's not easy raising a 15 yr old these days!!) Thanks again!