The most likely factor that led to the woman's lung cancer is radon gas emissions.
Radon is a naturally occurring radioactive gas that can accumulate in homes, particularly in basements and lower levels, and is a known risk factor for lung cancer. Since the woman has lived in her home for many years and there is no history of smoking in her household, radon exposure is a plausible explanation for her lung cancer diagnosis.
While other factors like combustion byproducts from indoor cooking can contribute to lung cancer, they are generally less significant compared to radon exposure in non-smoking individuals.