Why would the nun come to the house & say what she did?

They had a right to know. If you went to an orphanage to adopt a child and just so happened to pick the evil one, wouldn't you wanna know? Things like that way heavily on nuns.

She was concered but wasn't sure if she was really capable of killing them. Mind you, Esther was been in her care for a long time and admitted she personally never had trouble with her.