I've been reading some of the comments on the other post with this question and without wishing to add to the judgemental comments about prejudice on you or your niece's part, has your niece, or any of her friends, relayed any specific incidents, or conversations? It's just that I vividly remember all of the girls (including me) at my secondary school, especially between ages 11 and 14, labelling pretty much all of the men working in the school as pervs, weirdos etc.
This is a bit cod-psychology, but looking back I think this was because we found any adult male threatening. Hope you don't find this patronising, but it sometimes just takes one mis-interpreted look to get one girl spooked and she will get the rest of the group whipped into hysteria, and re-imagining past encounters. Same theory goes for all these allegedly lesbian PE teachers in schools!