My experience comes from Dirk's heart attack & bypass operation when he was 63. We were ALREADY low salt, not terribly high fat, low sugar diet, LOTS of veg & fruits & whole grains, he's an athlete -- but he had a heart attack (while fencing, of course), and then they went through this whole "learn about heart-healthy diets" song & dance. I exploded at the docs and said, WTF?!?, and they sheepishly admitted that diet really isn't that big a part of it, it's MOSTLY genetics (and smoking, & he never smoked). And his father's heart was crap.

Your mom doesn't need to make lifestyle changes for marginal benefit, it's not worth the strain on ANYONE. Focus on what can keep the stress levels for the whole household as low as possible, and remember to put one your own oxygen mask first.