Just my opinion, but knowing how CW thinks won't help spot the next one. To be sure, there may be similarities between one crazy and the next. But I think aside from the basic "flatline" of their personalities, each crazy figures out what type of manipulation and usage of people works best for them. All we can do is pay attention and listen to our instincts when our conscious and subconscious are trying to tell us something important.
I don't recall where I read a statistic (maybe the book The Gift of Fear, which I and others have mentioned before) about how we consciously are aware of a very small fraction of all the information available to us in our interactions with the world. Our subconscious picks up on a lot more info, which it feeds to our intuition, our gut feelings, the hunches we cannot explain.
We consciously try to explain away those intuitive, interior thought processes, to our detriment, usually, sometimes in small ways, and sometimes with severe consequences.
I think Shannan's friend who went to the house to check on her was listening to her nudges, and acted on them.