That, and while the decision to adopt was an unselfish one, the adoptive parents were certainly uber Breeders.
They had three older bio-kids and adopted this creature and her older sister when the creature was two.
Early on, they noticed something was wrong and she was more than they could handle, but they kept cranking out the bio kids, at least two more, according to the article.
If you are overwhelmed with the kyds you have, why keep having more? And in this case they were giving psycho-kid fresh meat to prey upon. I feel sorry for the other kids in the family, particularly the younger ones. You know when the parents aren't looking, they will bear the brunt of her behavior. And they are stuck with her as their sibling for the rest of their lives.