If the head has agreed that the actions of the TA did happen and yet does not see a problem with the behaviour of the TA, then yes, I would be going to the governors OP.
It doesn't matter what the child is or is not like, those of us in positions of authority have to abide by safeguarding rules and behave in a professional manner.
I can't see how people think it is reasonable to tell a child to "shut up" then put a hand over their mouth. If the TA had been behind the child especially, a random hand suddenly planting itself on your mouth would be scary. she's lucky she didn't get bitten
I get kicked and sworn at by dementia patients at work, doesn't mean I can tell them to shut up or lay my hands in them. No, they are vulnerable, just like children are vulnerable and in all honesty if the TA is so quick to lay her hands on a child then she needs to reconsider her career options.
We had one particularly terrible TA who was vile, we joke about her now but at the time it was awful. She spoke horribly to the kids and breached confidentiality several times as she was good friends with the mother of a pupil in the class. I'll never forget the time when she blabbed about a child in the class who had been sexually abused. She was privy to the conversation which took place between the parent of said child and the teacher and felt it was okay to tell everyone.
She also used to tell whose children had head lice. Poor wee kids were getting bullied as all the other kids knew they had them after being told by their clearly not so pleasant parents