It’s possible some other animal got to her first, and the dog was in guard mode after chasing it off, but the chances are likely it was the problem since she was just a visitor and not a member of the household. They are supposed to be extremely loyal to their family, and she might not have been considered part of its pack. May God comfort her loved ones. Grandma is going to feel guilty for the rest of her life.
There should be DNA in the girl’s wounds, and it should be species specific, and if it is from the dog, the individual dog’s DNA.
It is a disheartening tale, regardless.