When you fly an airframe at higher than intended altitudes there is a shift in the actual force of air flowing over the wing.

Wings need airflow over the wing to generate lift, and you can induce a stall in enough airflow over the wing even going very fast, if high enough.

Worse, there are speed limits to the airframe design, and as you go higher the stall speed and the overspeed speed become closer and closer together. The way the jet was flown these parameters would have been within a few dozen KPH of another.

A bank or turbulence or small deviation could then easily push the aircraft into either limit and past it.

When this happens loss of control can occur due to buffeting or ovulations of the control surfaces in an overspeed event. An original stall at too high an altitude could cause a loss of altitude but increased speed at a high angle of attack, again creating overspeed conditions with nose down.

The result in either limit being exceeded results directly in a follow on overspeed that rips the rear of the airplane control surface off, making recovery and flight impossible.

This is a classic and well defined flight parameters problem.

Over-speed. She said as much on the radio.

(Edit: things fall off airplanes when hey go too fast)

entirely conjecture at this point, but:

according to Captain Steeeve (a recently retired military and airline pilot) over on youtube, this same plane experienced several minutes of extreme turbulence a year or so back: https://www.youtube.com/watch?v=YtA657zwqBI

the implication being that the airframe may have suffered enough stress from that extreme turbulence that it contributed to this crash, elevator separation feels like it would fit

Yep it's a key piece