Hello, and welcome to the board,
There are many different things that could cause back pain in a teen. Where is her pain located? Was she injured in any way? Did the pain come on gradually or suddenly? Does she have any pain running across her buttock or down the back of a leg? How would she describe the pain? Is it nurab, tingling, electrical, sharp, like a bee sting, etc.??
If you could provide more details, I'm sure someone would have some ideas for you.