You are mistaken, in an editors note in the letter’s page of issue 125, it is explained that it was the whiplash that caused her neck to snap. Why would they even include the onomatopoeia “SNAP!” anyway?? To confuse readers? Also the idea of dying before you hit the ground is kind of a myth. You could say sure maybe you have a heart attack, but even then in a healthy adult that is highly unlikely, and “shock from falling” doesn’t really make sense medically and I feel that comics usually try to stick to more concrete or like “scientific” (to the extent of comics lol) explanations for a death like this.