That was the cause of her lung cancer, and her physician and medical examiner concurred.
"But she lived a relatively long life though, so that point is moot."
The point is that her physicians expected her to live to 100, and were it not for her exposure to decades of second-hand smoke (mind you, even 20 years after she was hardly around any), she would not have died of lung cancer. The irony is that her brother-in-law, my grandfather, smoked for nearly 70 years (from the time he was a child), and suffered absolutely no ill-effects whatsoever from his habit.
Could it be that the cancer in her lungs was just a mass that settled in her lungs, as they do in other parts of the body? Is lung cancer only caused by smoking?
Scan and post the death certificate stating cause of death as SHS.
You had a doctor tell you that with a straight face?
Call the funeral home and get them to make a copy of the death certificate and post it here; you'll make headlines.