Not speaking to her case, but it happens. My family moved frequently, which meant hopping schools in different states. As a result, I missed many 'required' m

Not speaking to her case, but it happens. My family moved frequently, which meant hopping schools in different states. As a result, I missed many 'required' math classes, simply due to coincidences of scheduling. (This was in the 80's, well before the current attempts at cross-state standardization.) In my case, it did not cause me any particular trouble, as I was able to teach myself what I missed. My parents had predicted that this could be an issue, so they made sure I had the resources I needed. But if they had not been proactive, I could have easily graduated HS without ever having taken certain core classes.