my mom still smokes after she got lung cancer?

my grandma was diagnosed with lung cancer a few years ago and we had to take care of her until she passed away. then a year ago my mom was diagnosed with lung cancer also, she went through chemo therapy and now its gone, but now she smokes again, is it highly possible that she can get lung cancer again? is she more in likely to get it again? or can she not get it again? please help.
smoking can cause lung cancer. the doctor said thats what caused it. and the same with my grandma.

What are the chances of getting lung cancer after 30 years of being smoke free?

My father is 80 and has not smoked for 30 years. He was just diagnosed with Small Cell lung cancer and will be undergoing an aggressive chemo/radiation therapy. Can an individual get lung cancer after not smoking for 30 years or do you think there is another variable causing the cancer?