Reading it again, it would appear that her main wrongdoing was not to stop other pupils discussing the issue. It is they who referred to the individual as 'that', and used the word disgusting, not her.
As we know, only too well, there are numerous pitfalls one can fall into when discussing this issue. Women have had to go to court, ffs, to confirm that even their opinions about this are allowed to be legitimately expressed.
My impression is that everyone was aghast at what was happening, but no one had the words to express it.
And there is every possibility that she felt that had she raised it up the food chain, she would have faced even more censure. No one can be unaware of how many women have been in that exact position.
As it was, it was the parent of a daughter in the tutor group, who raised it.