J.K.
I agree with Nina K. to try not to worry too much - it seems that from your description that these may be tension outlets or coping mechanisms that she has developed, in order to deal with stress or anxiety. I'm an MH professional & my dentist called me out on cheek biting as a kid. I still find myself biting the inside of my cheek without even realizing it on anxious occasions or when I am deep in thought. Sometimes kids who are on the "above-average" side can be prone to anxiety issues, and the resulting outlets. If she is doing this intending to cause pain, well, you might want to talk with her pediatrician, but I'd hesitate to start diagnosing anything - even though it is tempting. Keep an eye on it and if it still is a worry think about mentioning to her pediatrician at her next visit.