Maybe the person is also elderly. Maybe they thought NG was sick. There could be many different reasons they didn’t go themselves.This phone call to Annie is a bit odd. If this friend from church was concerned enough over NG not in attendance, why didn't he/she go over to the house themselves? It seems to me that this person who had Annie's phone number must also be quite a good friend.
Had they gone to NG's home, they would have seen the blood outside the front door and called the police themselves.
Maybe it's nothing, but it seems a bit odd in an already odd case.