Other mistake: Joyce is always wearing fresh lipstick regardless the time of day or early morning at wake.
Other mistake: When Emery awakens from his nightmare his clock reads 1:20 a.m. But in the following shot, a grandfather clock in the hallway strikes 2am, but its hands are at 12:00 am.
Chosen answer: It was actually the bloated corpse of Kevin that let Emery's mother in, so he wasn't alive when letting her in.
Bishop73