I don’t have any experience except an old partner had major issues with self harm and eating issues and anxiety. I am in no way saying she has any major issues, mat just be a bad day, and she knows you are worried.
Does her school have assistance you can speak to? to me it sound like you guys need extra help. I am sure she don’t even know all the emotions she is going through.
You need to assist for help as soon as possible, even if its nothing, because help can take a while to be arranged.