Plenty of normal, sober people die in their cars in water. Opening a window while the car is sinking means you now have water rushing in against you. The nose of the car sinks down and your body floats up and to the rear. You have to reorient yourself and dive down to get out of a window. The rear windows aren’t useful since they don’t open all the way. You can’t get the back hatch open becasue of the weight of the water and you have to dive down further to the front windows, and now the car is flipping over.
If all that happened while a person is trying to escape, try now imagining everything while being drunk, or high, or both, or on a psychedelic substance. If she did get the windows lowered in response to hitting the water, that doesn’t mean it would have been easy to get herself out of the car.