DID is Dissociative Identity Disorder. Most people know this disorder by Multiple Personality Disorder which was the name in the proceeding 4 DSMs. I had a sneaky suspicion that Mary was a part of Grace – her other personality – because I thought their relationship or the way Grace talked about it was a bit weird. Grace has a loss of memory during the murder and DID has a criteria where the person loses memory of everyday events or of a specific event in the past. It could definitely explain why she has no memory of it because she was not aware. Maybe Mary saying “Let me in”, was a way for Mary to take complete control over Grace. The quilt names for each chapter could also be symbolic of pieces of Grace put together to see all of who she is. You have no idea what the quilt looks like until all the pieces are put together.