The child was 10. 10 year olds behaviour cannot be predicted for obvious reasons such as immaturity which is why very important processes are in place to protect staff and pupils. Processes staff are trained in.
The childs misbehaviour would have been irrelevant, even the lack of resources, if the adult in the room had followed the clear processes to protect them both it wouldnt have happened.
The teacher is human, she made a bad decision and screwed up big time and a child was hurt, she admitted it. She deserved a written warning and retraining /supervision at the very least. The same would have happen in any industry where h&s is so important.