She did not die of natural causes. She died of Lung Cancer. I do not know what "caused" her cancer. We don't really know what causes anyone to end up with a disease because so many factors interplay.
A person can smoke and get lung cancer or not get lung cancer. A person can not exercise and stay healthy or exercise and stay mobile into their very late years. But it is not a crap shoot at all.
We have known risk factors and probabilities. It is possible to stack the deck in ones favor.
That being said:
- maintain a normal weight
- exercise daily (including strength training on 2-3 days)
- limit saturated fats, sugars, salt and empty calories (and sometimes calories in general)
- add fruits, vegetables, fish, whole grains and healthy oils to your diet
- don't smoke
- limit radiation (sun and medical)
- avoid environmental toxins