She may be a bit behind in her development. Put some bathmats down with the rubber up so that she can more easily get her balance. Could just be muscle development. Hope it's not serious. We invest a lot of emotional energy into these little guys and it's heartbreaking to see one that struggles.
It is way too early to be concerned. Relax and enjoy her. If she continues to exhibit unusual behavior, you can ask your vet about it at the well puppy exam at 7-8 weeks.
