Very importantly, he said bump shows up later not at the time when accident happens. It is exactly what I told startstart. It is the reason why the teacher ignored the poor girl later. she was not so cauitous to check her out later.
There was one person could help startstart if she really want to pursue this. That is the gym teacher. He, by startstart, obviously noticed the bump and communicated with the teacher. Startstart may want to find out what he will say about this case and start from there.
But it is not a right mentality to just assume the teacher purposely ignore the girl's bump. No one really buys it.