I was 66 when I had a quadruple by-pass -- eight years ago. Three arteries 100% clogged and a fourth 85%, but I had built up a pretty good collateral blood supply over the years (I had my first coronary episode when I was 34), and the damage done by that and the three episodes that followed was minimal. In my 53 years of addiction, I never smoked more than one pack a day, but I only got around to quitting the morning I went in for the surgery. I was a little overweight, coughed all the damned time, yet only occasionally experienced angina. For me, post-op, it was the chest that hurt, not the leg from which the vein was taken, and it hurt for well over a year. Wish they'd warned me about that, even though it wouldn't have altered my decision.
    My cough is gone, along with the addiction. I'm even more overweight; I don't do the 3 or 4 miles every day that I should because my back now bothers me too much. I take albuterol and atrovent by way of a nebulizer to cope with my COPD (didn't they used to call this emphysema?), but I'm alive and still functioning at my job. Quality of life? Infinitely improved. I genuinely believe that, were I wed to a walker and as physically limited as your mother seems to be, I would choose to risk the surgery.
    Any way you could get a couple of other cardiologists and surgeons to evaluate her chances? If she won't even let you talk to her doctor, this would appear to be impossible, but you might give it a try. My son's mother-in-law was denied a by-pass because her doctors felt she was too fragile. That was about five years ago and her condition has been deteriorating ever since, but she's still with us. She must have been about your mother's age when she didn't get the surgery.
    I realize all this provides no advice at all, and I'm tempted to simply erase the whole thing, but what the heck...
    Sandy