Revealing mistake: Winnie gets angry at her parents and runs out of the house. As her father stands up and she runs past the camera it wobbles, shaking the screen a bit.
Revealing mistake: When Winnie and Tuck are out in the canoe, and are being spied on, look at the shot that shows the profile of the guy's eye looking through the binoculars. His mascara is clumping.
Revealing mistake: In quite a few scenes in the movie, Winnie appears to be mouthing the lines of others.
Answer: It depends on the court. If the court believed killing the man was not necessary to save Winnie (ie. if a judge thought he was outnumbered and the men could and should have wrestled the gun away from him); then yes. A court could still find Mae Tuck guilty if they believe death was an excessive use of force in defending Winnie.