J.S.
Hmmm interesting. I would like to say it's just a phase and not to stress about it. But I guess there are some warning signs to indicate it's a bigger issue, like:
Is she obsessed with her hair for loooong periods of time?
Is she purposely pulling her hair out?
Do you see that she's pulling at her hair during times of stress (like, as a way to calm herself down, or as a soothing mechanism)?
Does she have any "hair rituals" that seem obsessive or compulsive to you?
If the things above are done IN EXCESS, and for long periods, I think it's something to be concerned with. At that point, I would contact a counselor to talk to regarding stress, anxiety, obsessive compulsive type stuff. (I'm a counselor, so my mind automatically goes there, but it definitely could be just a phase for her!)
Good luck to you!