Other mistake: At the end of the movie when the truck falls off the bridge and hits the water, the hood breaks off and you can see that there is no engine or transmission in the truck. (01:28:40)
Other mistake: In the bank scene, the monitor on the bank manager's desk goes from being connected and has a power cord, however when Kurt rises to go to the bathroom, the back of the monitor shows no cords whatsoever. (00:48:00)
Other mistake: When Barr arrives at his house it's still dark and his wife points out it's 6:00 in the morning... but considering it's summertime (proven by short shadows throughout the film and the heat in the desert), at 6:00 the sun would already be up or coming up. No dark sky exists at 6 AM in the summertime.
Other mistake: At the end of the movie, just before the credits, Kurt Russell and Kathleen Quinlan are leaning against the guardrail in each others arms as the camera shot widens. The destroyed truck they were in is against the rail and the roadway is shown. But there are no skid marks on the road surface. Their truck had been pushed sideways at least 50+ feet by the villain's semi tractor and there should have been skid marks from both vehicles.
Answer: She was not in on it. However, once she turned against Jeff by encouraging her son, Deke, to shoot him, Jeff suddenly felt her to be as much as a threat as the others involved. This would explain why he had her and Deke into the cellar to be locked up with the others. Also, don't forget she was startled to see the freezer and Amy popping out of it.