I wonder if it had anything to do with the long flight of the day before.
I have never heard of drifting before yesterday. I guess we do it sometimes unintentionally (and in slow motion) on our snowy roads in Michigan.
Sounds like DVT, especially if she flew coach class.
In the late 1950's I was a sports car nut. I subscribed to and read every sports car magazine there was. Sports Cars Illustrated was my favorite magazine. They always spoke of 4-wheel drifts when racing. I am not sure there are any real sports cars out there today, but back then 4-wheel drifts were commonplace.