I went to an independent school with a fair amount of notable alumni and apart from coming in to give a few speeches about life after school, most people don’t look back. There is an old girls association that holds various events but none under the age of around 30 bothers. There’s nothing wrong with keeping in touch with your old school (I did work experience in my old primary school) it’s just that Ruby seems to like going back to act like a school girl again, not an adult talking to actual school students about her life after school. Also her want to find out who the head girl is every year is weird, tbh head students don’t really do that much, as far as I’m aware, it’s a great achievement but not something someone who left years ago should care about. If there was a Ruby at my school she would’ve been a laughing stock amongst students and some teachers.
I mostly went to state schools, but got a bursary/scholarship to go to a boarding school for the GCSE years. I have to second this post - it's not normal behaviour, even at private schools where 'networking' (I hate that word) is more common. Speaking from experience, it would be normal to:
-go to alumni events, e.g. dinners or class reunions (though the people attending these are usually a lot older, i.e. a few decades removed from their school days).
-maybe add a teacher as a Facebook friend once you've left the school.
-return to give a careers talk if you've done something interesting. I remember a professional golfer, an aircraft engineer, and someone who'd gone to do aid work in India. They would never invite themselves to do the talks, though; it's organised by the school.
-go to a fundraiser - but it wasn't a frequent thing.
-one girl returned for a year as a P.E. instructor because she was aiming for a job in sports coaching iirc.
Nobody would randomly turn up at the school after they'd left. I actually don't think it was allowed unless you had a good reason to be on the school grounds. Even the scenarios I've listed weren't that common. I went back to this school two years after leaving (to sit an exam) and needed a background check! Returning wasn't a fun experience either because none of my friends were there & I felt like a stranger in a familiar place. Also worth noting that a lot of the boarding students went back to their home countries and my friends were more likely to visit former classmates in these countries than go back to school.
I'm sorry this post is so long and rambling. I just can't emphasise enough how bizarre Ruby's head girl comment is, even by her standards. It's unhealthy and creepy behaviour.