My MIL has lung cancer and is facing a long battle with chemo and radiation but the doctors say there is hope for recovery due to where the tumor is. However, she has become very depressed...won't leave the house (she was previously active and has no physical limits at this point); doesn't want to do things she normally does, etc.
She has had a history of getting off again, on again depression. Also there is a history in her family, i.e. her uncle committed suicide, her daughter is often depressed, her mother was often depressed. Don't know a thing about this, i.e. if it's family-linked, etc.

Does anyone have advice on what could be done, either through non-medication or medication methods? I know nothing about this subject....

Your MIL should most definitely speak with her physician about this. There are lots of meds out there: Wellbutrin, Xanax, Prozac--she can get help. These meds take a long time to "kick in," so get her to see her doctor pronto. She is undoubtedly very afraid, after all, who wouldn't be. She may be thinking that it's not worth fighting, and her mood could cause her to refuse treatment. Each has his/her own battle with this decision. Help her to recognize that she can be helped and that the family is right beside her. Tell her how much you love her and how you will all be right there to help her and she will feel much better if she can ease the depression. It's as bad as cancer.

Mary