I remember when Friends Reunited was a thing, one ex-student from my year at school said she always felt uncomfortable being made to swim lengths privately in t-shirt and kickers as punishment by one particular male PE teacher whenever she forgot her swimming costume.
Others replied with "OMG - that happened with me too!" and various others chipped in, some pointing out that the teacher's wife (also a teacher) would sometimes join him to watch these private swimming detentions, and that the memory of it was all very weird.
As a boy at the school, I remember this - because I was once sent to give that PE teacher a message, and walked in on one of these "detentions" and remember thinking it somehow didn't seem at all "right" to me.
Friends Reunited seemed to throw up a lot of odd-sounding memories from (now adult) ex-students across the UK, and shortly afterwards, moderators started posting a lot of warnings and doing deletions if I remember correctly.
Anyway - that's just a long-winded way of saying that, as a parent with girls, I would definitely follow-up on this, and I would do so in-person rather than by email or phone, as it's a sensitive discussion.