I was living on my own at 18 years old and I'd have been furious if my parents started getting involved in my personal life.
This with bells on. I was living on my own, working, getting professional qualifications at night AND a single mother to a child when I was 18.
Mumsnet has such a warped view of... life. Just actual real life in general.
It doesn't sound like this woman (yes, woman!!! Grown, adult, woman) is addicted to drugs or been trafficked or abused or neglected or fallen on desperate times or anything else. She sounds clever (top performing student) and comfortable (parent's paying for living expenses).
I hope the police / social work / NSPCC / fire brigade / army and whoever else MN advises you to contact tell you that.
Is it great? No. Is it what I'd want for my daughter at that age? No. Would I be doing everything within my own power to talk her out of it? Yes, absolutely. What mother wouldn't?
But to say it's safeguarding or illegal (someone mentioned youth offending team - WTAF!) is madness. I know a couple of girls, now women, from school who went down the whole OnlyFans, AdultWork, Party in Dubai during Covid line of work (with no addictions or abuse driving them into it) and they're all perfectly content. And loaded.
I wouldn't want my daughter doing it because murder statistics, but I wouldn't want her to be a soldier either. I especially wouldn't want her working on a farm, those death and injury statistics are scary. Yet at 18 she can legally do all three.