According to Av. Herald, SWA is claiming they lost it in attempting the 90° turn-off to taxiway (as your story says also).
I will say I was out in the back-end of the same snow event here in Denver, and it was lethal stuff. 1/4-inch of transparent freezing slush over a 1mm sheet of ice, even in "cleared" areas. Worse than a skating rink for walking.