My 3 year old and keeps grinding her teeth.what can i do to make her stop?

Very little: You can remind them but it is not easy to make them stop and though they make appliances, it is not likely the child will leave it alone or in for that matter.

Common problem: This is a common problem in children. Unfortunately there is no common consensus about why this happens or solutions. The current thinking is that it is due to breathing constriction. This constriction could be due to children having smaller mouths, some children having larger tongues, allergies, sinus problems, stuffed noises, or tonsils. Many children do outgrow grinding.