She died of stupid, the release is literally right on the door. It's not hidden, obfuscated, covered, or in any way shape or form difficult to use. Just another idiot that didn't bother learning what all the controls on their new card did.

That being said, even with a manual release they most likely would have died anyway. As once your car is in the water unless you're able to open the door basically instantaneously upon hitting the water you're going to find that the door is impossible to open as the weight of the water will prevent it until such time as the car has filled with water to equalize the pressure. Generally speaking people that survive cars falling into water were able to get the window open, or just break it entirely. The door is almost never the Escape Route as it will not allow itself to be opened due to the difference in pressure

Edit: turns out this is only in the M3, the Y, X, And CT are all designed by absolute idiots, and i joined them by not looking into all models