we see alot of teeth grinders at work, usually its completly harmless, although sometimes can cause jaw stiffness, or can also cause excessive wear especially in front teeth, and can also cause teeth to feel tender & sensitive in adults, kids generally will do it occasionally & most will grow out of it, adults can have a special mouthguard made up out of really thin clear material its quite hard which they can wear at night to protect their teeth and also stops the awfull noise, you could possibly get one made up for keira but i think they may be reluctant to do this with her being so young, if you do get worried tho take her to see a dentist about it or a dental nurse, although most dental nurses wont do anything but they can give you a referal to see a dentist which means it would be free otherwise you would have to pay a consult fee which could be as little as $20 or lots!! depending where you live.
but she may grow out of it in a few month
sorry for the novel
hope some of this helps