Hi J.. I am a newly graduated dentist so I looked up your problem to be sure I had my information correct. Here is what my Pediatric Dentistry book has to say:
Treatment should begin with simple measures. Occlusal interferences should be identified and equilibrated if necessary. If occlusal interferences are not located or equilibration is not successful, referral to appropriate medical personnel should be considered to rule out any systemic problems. If neither of these two steps is successful, a mouthguard-like appliance can be constructed of soft plastic to protect the teeth and discourage the grinding habit. If the habit is thought to be due to psychological factors, which is unlikely, referral to a child development expert is warranted. Rarely, occlusal wear is so extensive that stainless steel crowns are needed to prevent pulpal exposure or eliminate tooth sensitivity.
So there you have it. The most recent text edition of Pediatric Dentistry as taught at the University of Colorado School of Dental Medicine. If the grinding doesn't resolve on its own, check with your dentist to see if there are any interferences that can be relieved (a tiny bit of grinding - no injections/no pain) or a mouthguard if her teeth are wearing faster than her natural tooth structure is replaced (not likely necessary). If you want to contact me for further questions I would be happy to respond. Dr G.