my suspicion is the air bag + unbuckled seatbelt strangled (drowned) her to death under water. I heard recently a driver died in an accident because could not unbuckle the seatbelt and escape the fire blowup.. My general understanding is the seatbelt and airbags can minimize the impact injury but can also become 'anchor of death' in some cases. I wish the airbag blow up can automatically trigger the seatbelt unbuckle? Can we really control the time of death?

I've seen seat belt cutting tools with combo glass break (if the car is submerged you will not be able to open the door until the pressure is equalized.) which you keep in your glove compartment From what I have read, the seat belt cutting tools are virtually useless. Seat belts are too tough.

From the video and pictures of this accident, the "water" is more like a drainage culvert along side the road. My guess is that the water had nothing to do with the death. As someone said earlier, it is odd that a rear-ender would cause so much mayhem. The difference in speed must have been extreme. It's a straight road -- maybe she had a medical event first?

I know someone that drowned along with 3 others in their upside down car because they could not get out.

Airbags don't lock you in except at the moment of impact. The bags are not even remotely airtight and deflate almost as fast as they inflate. Seat belts however will lock you into the car so folks have at least 2 good quality high visibility emergency seat belt cutters/glass breakers in the car (so you have a chance of finding, reaching, and using one in case of accident that locks you in).