We are not Vets so please if you are really concerned take her to your Vet. My opinion is that she is dreaming...puppies dream quite a bit and they will twitch and their little legs will seem like they are running after bunnies...
they also get the hiccups
...but, if you have concerns that it is something more serious please, take her in.
Welcome to pets, if you have some pictures of her doing this it would also help
, we love pictures here....patti