I suppose it's possible she had noticed her husband fell asleep (or had a health event?) and unbuckled her seatbelt to reach over to the driver's side petals to stop the vehicle. It passed across the median, so there could have been time for such a scenario. Or not. The kids would obviously know.
But yeah, people that don't wear seatbelts blow my mind. It took several years, but my wife's family finally buckles up in the back seat now without me having to ask