A four-year-old grinding her teeth at night is normal. Her permanent teeth are pushing toward the surface, and this grinding action is involuntary. It is the process by which the primary (baby) teeth remain in the proper occlusion and eventually wear away to make room for the permanent teeth. There is nothing to be concerned about. Of course, if you have to listen to the grinding all night, it can be very annoying. Not to worry though, she'll probably outgrow this condition by about age 10-12. ;)
TRY Google--type in "bruxism". That's the technical term for teeth grinding. Many times it's caused by "reflex chewing activity". Check out info on bruxism. If it continues when she has her permenant teeth, there are mouth guards available (also called bite guards). Many people grind their teeth, sometimes to the point that they wear them down flat! Best to You! <<<ADR>>>