Consider Pancreatic Cancer, fourth largest cause for death in the USA, eighth worldwide. Peak age is 75, but it’s not uncommon in 50 year olds. There’s some speculation that 20% of Pancreatic Cancers may be related to smoking, but this is not certain, and you can make your character a non-smoker. No other preventable causes have been found, so your character cannot be held responsible. A family history of Pancreatic Cancer is felt to be a risk factor, but this cancer is not a genetic disorder. At the time of diagnosis, most patients have only 6-12 months to live. The 1 year survival rate is 25%, and the 5 year survival is 6%. Treatments are limited, and mostly ineffective. Pancreatic Cancer would provide a wonderful set-up for a character to re-evaluate her world in the final tragic months of life.
H.S. Clark, MD