Is it normal for a 4yr old to grind her tooth while eating? this is something new, she wasnt doing that before. also while sleeping? how to stop her from doing that?

The enamel may be affected, and the habit of teeth grinding may be modified. Discuss whether a behavioral therapy consultation is recommended, with your pediatrician. Maintain good dental health and please follow up with your dentist.

It is actually quite common. No worries. Not really possible to stop it. Only primary teeth are affected at her age.

Most children grind their teeth at one point or another. Many because they "back up" their internal computer (brain) while they sleep. Also faces grow in different locations on different days, and they are simply grinding-in their occlusion. Usually spontaneously resolves. If it does not in just a few months, advise that you see a pediatric dental specialist, a Pedodontist.