I think a lot of children do this, and it is simply a comforting movement she is somewhat young for it to be anything much else,I guess it is always good to be aware of any thing differant in her life at any age, make sure you know the persons who babysit her, too often one hears of small children left with ,even pre teens, and they real;ly dont have the skills or know much about CPR.
Yes But I doubt if it has the meaning that you are saying "Dry Hump"//