Horse Crushed Aunt.. Should she have died?

Hi, one of my friends Aunt have been riding all her life, she owned a 2,500 pounds clydesdale gelding, gentle as can be, he was a great jumper and could jump pretty high! she was jumping him a 1.5 meters and suddenly the gelding collapsed, it landed on her and rolled on her.. my friend and I are devastated as her aunt is the reason why at 3 years old I started riding and now why I am almost an olympic level jumper and own several of my own horses, (I am fifteen), is that a reasonable way for her to die, I know the gelding crushed her but what happened that caused her to die? ( She was 37..)