T.,
Hello. I know with my own daughter she chewed on her hair for comfort reasons, when she was nervous or just thinking. A lot of times she didn't realize that she was even doing it. I realized she needed to have a re-placement thing. So, we talked about when she was a baby she use to love taking my hair and rubbing it on her cheek to relax/comfort her. She likes hearing stories of when she was a baby, so she agreed to just take the ends of her hair and rub her cheek with it. So, after that when I'd catch her with hair in her mouth, I'd just say "Are you rubbing it on your cheek?" She'd say, "Oh, yah" and correct it. That took a good 2 weeks of reminding, but that's what she does now. It's maybe still not ideal, but it's better than chewing on it. Find something to replace her habit with that you both can agree on (she needs a self-comfort thing). Hope that helps. Good luck.
~ J.