It's easy to go and blame the childhood, but sadly, for people like Hamber, I think it's a very conscious decision. It's literally fucking impossible to ignore the fact she's ruining her body. She spends all day reading about the shit killing her, so she can make vague excuses it doesn't apply to her..and in some idiotic 'I'm better then you!' she does shit tok ill her self quicker to..prove haters 'wrong'.
She isn't dumb in the sense she's handicapped either for reading etc. She clearly can read, I think she can easily comprehend what she reads at times. I also think she refuses to care. She has nothing to live for, so why would she bother??