what a heartbreak! She must feel devastated.
You have really got to know how your dog reacts when the door is opened. But there's always that one time they do something different, like this Chi. Very sad.

(all 3 of mine are different- Star waits, Sherman wears his leash & I grab it before he jumps out, and Speeo is tied so he can't jump out at all. ) We go in the car almost every day.