My God screwed up making her and now Darwin is taking over. It is no accident that she was made of such faulty material that God didn't want to pass it on. Also she has a brain tumor. Again, faulty material. Sure, her parents think she's perfect, but now, it's her peers she's has to live with.
She is good, but not great, and it can be painful to be merely good in the midst of greatness, and with a brain tumor, one can only cling to the fantasy of greatness. Fantasizing can be better than realizing.