All four wheels locked up while driving.

My wife was driving our 2012 S/c when all four wheels (at least that is what it felt like to her.) locked up on her(on a wet road, luckily). She was quick minded enough to throw it into neutral and coast to the side. Now it will not engage into any gear. The shifter moves it into the gear , but all you get is a bit of grinding and what seems to be the transmission spinning. She was accelerating through an intersection (left turn) when this happened. Had it towed to the shop....waiting. No check lights, but the 4dcan gave a bad or implausible speed sensor ( I forget which one). My knee jerk reaction leans toward a bad transfer case. Any ideas would be great!
Thanks in advance.