I am a secondary school librarian.
IMO all school libraries should be run by trained librarians who understand the safeguarding policy that their school will inevitably have. They should also be using their school library management system (catalogue and circulation system) to record information on the content of heir books and the age limits.
I had a 12 year old borrow a Stephen King book this week, they were only able to do so because their parent signed a form I had given them to take home.I have loads of manga I would not loan to an 11 year old and there are plenty of books for Y10 and above. Having these restrictions set on the circulation system means that my school librarians cannot loan inappropriate material either.
There’s also budget considerations. Do I want to order yet another badly written book that no one is going to read about magically transforming from being female to male - nope - and the decision on that rests with me. I have plenty of books with lesbians and gay characters, some with trans characters, I have some books with sex scenes and rape (A color Purple for example) but they are not appropriate for every child and I have to make decisions based upon content and what will be borrowed and by who.
Game of thrones is not appropriate for younger readers. Heartstopper has language in it that is inappropriate for 11 year olds, even if they know all the swear words already.
sounds to me like the librarian in this case did not have a robust policy in place and maybe failed to monitor what she was loaning and to whom.
frankly it amazes me when school librarians think they can loan any old thing to any old child and not have any concern. Schools generally share appropriate well-being information about their pupils with their staff and frankly it is a safeguarding issue that needs to be noted by librarians.