I would also say growing pains , and get it checked out, seems to be a lot of it around this year, has she any fever, or other symptoms ?
It might be growing pains. My son gets those sometimes and wakes up in teh night crying. It can be so bad for some kids that they have trouble walking. I know a lady at work and her son had it really bad and it would be hard for him to walk, etc and he would wake up every night for a while crying.
Ifyou are worried run it by your pediatrician, just to be safe. I'm sure they ahve heard this before.