It has been speculated before that maybe the perp(s) was/were known by either Sherrill and Suzie, or by Suzie and Stacy....it's possible somebody was in that house and Cinnamon may very well have been ok with it.
Case and point....my wife and I have two big American Akitas that live in the house. We live on a corner lot, and our bedroom window is near where some of the neighborhood mailboxes are located. One night at 2am, an unfamiliar Kia minivan stopped there to top off his coolant. Our male went balistic. However, my brother keeps a lawnmower at my house, near this same corner of the house. He keeps weird hours himself, and can pull his pickup into our driveway, walk to the back gate, let himself in the yard, get his mower, load it up and leave....the dogs don't even acknowledge he was there. Sometimes, a neighbor simply walking by on the side road will get the dogs upset....and it's usually the same guy. Other people can come and go with no problem.
My point is, dogs have a sixth sense about people....depending on who may have possibly been in Sherrill's room (purely specilation if ANYBODY was there or not), Cinnamon might not have picked up on any danger until after the situation changed....
Entire (lengthy) post is speculation and my opinion only.
-Curtis