thanks for the comments everyone.and no it dont happen when shes upset it happens pretty much whenever theirs no certain time and nothing that causes it.she just does it.
I have seen children hold their breath till they go red in the face ,it could be something similar ,is it when she gets upset as you could distract her before she does it each time maybe break the pattern ...
It sounds like something my nephew used to do - and they'd say oh Dave's being intense again. It sort of looked unusual - but apparently he grew out of it - he's 19 now and fine.
Best wishes.
Hm. Well, it seems to be something she is compelled to do. It is an impulse that she is getting something out of. It is either soothing/calming her or waking her up. I'd say that I'd let her do it but think of other things she could do to get the same feelings in a better way. Lifting something would stretch that muscle like that. Mention it to your doctor on your next well check or sick visit or give them a call. Stimming is something some kids do. I don't know from your description if that is what is going on. But I would not make her stop as it seems to be an internal need. good luck