For me, the one thing is the dog - kenneling the dog.
Anyone who has a dog knows that, alone in a big mansion, in a time of trauma, you would keep your dog with you. Unless your boyfriend ordered you to take it to a kennel because he blamed the dog and you for his son's accident.
Conveniently, the dog could not bark. I believe whoever planned this planned the entire prolonged torture of it. They could have just shot her and tried to stage that as a suicide. But instead, they played out a sick fantasy that they'd probably had for awhile, with the bondage elements, doused with a little staging ala Jeffrey MacDonald and the note on the wall, and based on what they thought had been done to Max (suffocation). I believe they incapacitated her enough to tie her up but wanted her to wake up long enough to wake them paint the note as a taunt, and then to let her know she was about to be tossed off the edge.