I was rafting in New Zealand in glacier fed rivers and went in and shock is the right word for it, I'm an experienced surfer and was wearing an life vest and fully expected to go in the drink and it still just instantly stole all the air out of my lungs. I can't imagine what it would be like if it came as a complete surprise and you were not dressed for itIf she’s gone into icy water, she may have suffered respiratory failure - cold water shock. This can eventually lead to cardiac arrest due to the shock.
Even the most competent swimmer can suffer in extreme cold.
Exactly. The most logical hypothesis based on the evidence appears to be correct.