People can die young (age 65 is not exactly a spring chicken BTW) for any number of reasons, besides "living a hard life" as you call it.
I almost died of a heart attack at 63. Had to have quadruple bypass open heart surgery to save my ass. And I never drank or smoked in my life. Exercised and watched my weight. But is was genetic and ran in my family.
Some people die of anomalies, strokes, disease or infections. She must not have lived too hard of a life if she just returned from a walk.
May the poor woman Rest in Peace.
Lucille Ball died from an aneurysm. I think it was a ruptured aorta.