There’s a 15 year old in my class and she’s dating a 20 year old guy, advice please? ❤️

So there’s a girl in my class, (I go to a school for children with illnesses so there’s myself, my boyfriend, and this girl) this girl is constantly bragging about this boyfriend of hers and it’s really annoying and concerning. When she comes to school she’s always on the phone to him, but he’s 20 years old. Social services know and the teachers at my school know but no ones doing anything. It’s because this girl is saying they’re not ‘technically together they’re just talking’ yet when there’s no teachers around she’s always saying how small his dick is, and that they have sex all the time. Neither me or my boyfriend want to know that she’s having sex because we don’t care. But what we do care about is her safety. This girl has had a baby at 14 anyway but didn’t keep it she put the baby up for adoption. She has no common sense and is having sex with a 20 year old. But no one cares, I’ve told the teachers and they know but are not doing anything. Any advice? ❤️