My daughter did that. I told her to stop or her hair would break and she didn't believe me. The hairdresser told her that she would have a bald spot and she finally quit. I do it too. It is a nervous habit.
Sounds like stress to me. Why not do homework together and make it fun. I help my 10 yr old everyday and if he doesn't need help I still sit with him in case he has questions. So make a homework date with her if possible or tutoring.