Smoking is certainly not the only way to acquire lung cancer, it’s merely the most popular. She might have spent years living in an apartment that used asbestos for insulation, very common for the boomer generation.
At any rate, I am sorry to hear about what you and her are going through and I wish both of you — well, I’m not even sure what to say here without sounding cheesy or cliché — but whatever is needed to make this journey more bearable.
You're not alone. The human body is an amazingly complex and intricate series of systems, and watching them fail in your parent one after another is.. One of the worst things I have ever witnessed.
Like some illnesses just affect a specific area or part of the body, like when you break a bone of have the sniffles, but this? It is... very "creative" in the destruction of your loved one.
I wish your mom, yourself, your family, the best of luck.