Hi there,
Congratulations on your little bundle of joy!
Our little guy (now 9 months) was constantly scratching his head, leaving bald spots and a rash! We took him to a dermatologist, thinking he was pulling at his hair and scratching because he was feeling itchy. The dermatologist said at his young age babies don't scratch as a reaction to feeling itchy, so it must be an emotional behavior. But he did prescribe cortisone cream for the rash. I didn't buy the cream, put those little cotton hats on instead (like Tracy M. has suggested) and the rash cleared up by itself. Keeping the hats on was a bit challenging as he scratched away, but they did a great job protecting his little head.
My husband would put his head next to our son's when he was scratching/pulling his hair, and he would grab my husbands hair instead. That kind of proved to us that it was an emotional response, not that he was trying to scratch an itch.
He was also very colicy and had digestive issues. Perhaps your daughter's grunts and frowned are a reaction to tummy pain, not to hurting herself from pulling her hair?
It took him a while to outgrow the head scratching/hair pulling habit, but now we recognize he is tired when he starts to go for his hair. (I think the poor guy was overtired and we didn't understand because his big sister slept so much and just nodded off whenever she was tired, but he needed help falling asleep.) Maybe you can try to get your little girl to sleep more, as soon as you see her pulling at her hair?
Now we have to get this guy to stop pulling his big sister's hair!
Good luck!
Oh, and it will grow back, if she is pulling enough hair out that you can see it. I was worried about permanent balls spots, but his little head of hair looks great now. :)