I didn't get to see either of the last 2 matches, however, based on the what I read here and seen in previous matches, Shook just isn't mentally tough enough. She seems to have plenty of physical ability, but she gets rattled to easily and starts to play not to make mistakes instead of aggressive and freely. And is the case in most sports when you go into that mode things typically turn to shit.
The setter has to be your mentally toughest and fiercest competitor. While hitting and passing require plenty of technical skill, there is also quite a bit of instinctual reacting. Setters have to be able to think fast and make good decisions under pressure, just like QBs and point guards. I've seen pretty good setters just lose it and get the doubles like a golfer gets the shanks.
I wondered about Shook when she decided to stay home before her freshman year and play club ball. Contrast that with Eggleston, whom looks to be a future star.
There are plenty of problems with this team right now, youth, passing, blocking, serving, but these things can and likely will improve. Unfortunately, I'm not sure setting will. The stage might just be too big for her. I certainly hope I'm wrong.