This doesn't at all support the assumption she was "on alert" for the entire time. Ie, peering out the blinds with her eye on the house all day? She was recovering from surgery..
I must say also, that the question of how Cook could have entered the property without being noticed is a very good one.
I think it's possible -somebody- could have -- I live in a high-density area, and my neighbour's property is literally ten feet from where I am sitting right now, with a clear view out the window of the pathway. However, I don't keep tabs on who comes and goes - and several times I have been surprised by her son making a sudden noise on the other side of the fence - I did not see him arrive. Because I don't watch my neighbours -that- closely. Who does?
Well I guess you will just have to investigate that for yourself because me telling you is not going to be of any use.
I know the area well. It is not high density -it is a quiet residential area and if you were home and awake - and the neighbour was and she could hear the dog crying she'd hear someone drive up into the driveway across the road.