I agree with redcrx, distraction is the best idea with grinding teeth! Unfortunately I cant do that with my daughter as she does it in her sleep (just like I have always done! lol)
Remember, these are her milk teeth and it will take years of grinding for enough damage to be caused for it to be a problem. If you can get her out of tha habit, as Im sure she will, then you really have nothing at all to worry about. As I said, my daughter grinds hers at night. She is now 6 and losing her milk teeth and has regular visits to the dentists and her grinding hasnt caused any problems.