She is his younger sister and while sure these things she's said are mean, but everyone has a breaking point. She needs someone to look up to and her brother is destroying that possibility. I'd have more sympathy for the brother if he did some good for himself, but he's obviously not, from what we can tell. She just wants some help on helping him.
@OP: I suggest talking to your extended family about this, maybe stage some kind of intervention? Maybe one of them will let you move in?