Isn't the gear selection on the 7-speed completely electrical/electronic? The car likely dropped into drive while idling, that's why the wheel was turning. It would also explain the doors locking. Maybe somebody bumped the shift selector, maybe high-centering on a snowbank messed up the electrical system.

My money says she was gunning the engine in an attempt to drive out of the snowbank. The tire overheated or was otherwise damaged, and failed at high RPM.

How do you high center a 4-matic vehicle, anyways?

- JimY