L.M.
My son does this every now and then. Now that he speaks well, he tells me that he had a bad dream. When he was 3, he would do the same thing. He would cry and ask me to lay next to him. Then he would move around in the bed, toss and turn. Later on it became less and less. Now it happens every now and then as I stated before. When it happens I ask him what happened and recently he told me he was dreaming about a giant dinosaur. I told him that dinosaurs are extinct and they are no longer around. He looked at me and said oh. He is getting much better with this, he can go back to sleep without my help.
I would assume she is having a bad dream and don't know how to express it. I would ask her if she saw anything while she was sleeping. Just see what she says.