One Student Does Not Have Content Library in her class notebook

If her name isn't appearing in the Members list but she already has a personal section, that does point to an account or membership sync issue rather than anything she changed herself.

I've seen this happen when a student's Microsoft 365 account or class roster membership doesn't sync correctly. Usually, removing and re-adding the student to the class (or having IT repair the notebook membership) resolves it. It's also worth checking that she's signed in with the correct school account, as using a different account can cause sections to appear missing.

I think involving your IT department is the right next step, since they can verify the roster and permissions from the admin side.