I've got to agree. At least on the timing. That was the exact point at which something changed with her. As you said, you could see it in her interview with Greta. A lot of us commented on it at the time.
Personally, I don't think it was the book itself that did it. I believe that the book was only the public face of some other, more sinister thing the public wasn't privy to. In my opinion, Sarah didn't decide not to run - she was stopped.