Even the toughest, most determined player knows when they "really" have a chance to play. It's pretty clear in practices and in games.
My belief, which is just my opinion, is Shaina could have done everything right in practice and still would never seen the floor. She did some pretty decent things the last time she played. She tried to defend (and she's just as good at defense as anyone else on this squad, as far as I can tell from watching and re-watching the games). She scored in double digits in a very brief span and she still did the same dribbling into the lane and putting up a shot against three taller defenders. She also passed the ball more than she did before being benched.
Ultimately, she challenged the coach, and whether Sherri is right or wrong, when you challenge the boss, you aren't going to get paid or played.
Everyone saw the writing on the wall, why would she not be able to figure it out? Her attitude on the bench clearly indicated to me she knew what the score was and was going to be.
Looks to me like Sherri made it pretty plain from the get-go.