I've heard that sometimes the uterus, returning to its normal shape, can feel like a kitten moving. It could be that, but might not be.
Sometimes labor does stop. If the queen is resting comfortably, it's usually okay, but since you think there may only be one kitten left, that is a little strange. I've heard that up to 24 hours can go by before a queen delivers another few kittens--some people think it's that they've emptied one uterine horn, and take a rest before emptying the other.
Whatever the case, it's a good idea to take her to the vet anyway, to make sure she has no retained placentas or, as you're wondering, a kitten.
I hope everything goes alright! And to answer the question of Roimata, yes, sometimes kittens are stillborn. There are a lot of factors that can contribute to it, but it's not uncommon.
Good luck! Got my fingers crossed for ya.