When we see Casey smashing at the bedroom door it constantly rattles and shakes madly, but when we switch scenes to the other side of the door, with Elaine leaning on it, the door is not moving at all.
In the ending scenes when Casey and her Mom escape in the Volvo and come across the crashed Range Rover, it is steaming as if the radiator is broken, but there is no damage apparent to the car other than the hood being up. The hazard flashers are also on, would the Dad really have had time to do that? When the Volvo crashes into Chloe and crushes her against the Range Rover, her body slides down, but in the next shot it is feet away from the car to the side, the Volvo is also completely undamaged despite having crashed into a Range Rover with a tow bar.
While Casey keeps smashing at the locked door and apparently partly breaking through it, it seems her actions also opened up the lock magically. Also Elaine should be still sitting in front of it, however Casey is able to open it the outside way without any obstacle in the way.