The Other Mother is an entity behind the little door you found. The door is bricked off in the mornings, but at night it’s open. The Other Mother looks exactly like your mother, but she has button eyes. She acts like your mother, too, except she’s so much better. She takes the traits you wanted in your mother and portrays them for herself, acting as a “better mother”. The act is to lure you in to sew buttons in your eyes. Sleeping in the Other Mother’s house brings you back to your house.