Shiv and Kendall's Decisions in the Finale

I've seen a lot of different takes on Shiv and her decision in the finale. Some people say that it was preplanned with Tom others I think myself what I saw was her sort of in the moment making a decision based off of Kendall's reaction specifically his lie that he was not involved in the vehicular manslaughter. But beyond that but it was a very impetuous shift and seismic shift so I never felt that it's solidified into anything concrete. It was always going to be how could it not be. As soon as the reality of that ticking clock came down to actually putting our hand in the air one way or the other then the sheer reality of that started to erode her