This is known as tricotillomania and it can be something she will do for the rest of her life unless you do something now. I started pulling when I was 6 and still am at 25. There are many sites for parents of children who have the start symptoms of tricotillomania I would suggest getting on these sites and seeing what you can do. My parents put me in therepy didnt help and docs gave me all kinds of meds didnt help and made me feel worse I found if I put my hair up pretty or so that I loved it I wouldnt pull so try to find something she likes about her hair and work really hard to keep her loving her hair so that she wont want to pull or unfortunatly one way is to shave her head untill she forgets about pulling. It is a form of OCD and so if you take away what she is doing by shaving her head she will have to find something eles to obsesse about and with any hope she will forget about the hair. The best of Luck and really hoping that this helps you!!!!
I would mention it to her doctor and maybe seek a dermatologist.