To clarify - the person presented in the book could be diagnosed. Cheryl - today, in person - may or may not be.

All mental health diagnoses are clusters of symptoms that are merely abnormal duration or severity of things common to all people. They are only diagnostic criteria if they occur to the degree that they are impairing.

If you are taking umbrage to the suggestion that she was diagnosable, that's understandable. There's still a lot of stigma involved with mental health issues. To me, it's an indicator that we're all human.