I would call Child Welfare Services and just make a report. They have to investigate. If the girl has some kind of special needs that aren't being addressed then that would be considered neglect and the social worker can at least plug the family into appropriate resources. It can't hurt to express your concern and see what happens. It seems to me like the family is in denial and the girl needs help. As the mother of a special needs child I think getting help for the kid is the best thing.