Did anybody catch how La Femme got into the house?
In the unrated version at about 24 minutes in while Sarah is on the couch being interviewed by two of the three officers who first show up at the house, La Femme subtly slinks in through the front door which was left ajar by the officers. This is done so subtly that you miss it the first time you view it. It's on the periphery of the foreground scene taking place in the living room, so you may even assume it's just another officer coming in, but if you look closely you can see that it's her. This is how she got into the house.