Lung Cancer Diagnosis and Symptoms

Hi Everyone,
My 66 year old mother was recently diagnosed with stage 3 lung cancer. She spent months fighting pneumonia and fatigue before finally getting a diagnosis. The cancer has spread to the lymph nodes in her chest as well as a large tumor in her left lung. This was a very surprising diagnosis for us because she lives a very active, healthy lifestyle and has never been a smoker. She has chosen to undergo radiation treatments along with naturopathic treatments. She did do one chemo treatment and it made her so sick that she decided she wasn't going to do that anymore. One of the things that's really bothering me is that she is so completely fatigued she literally does nothing but sleep. She has been this way for a few months. I am wondering if this is something normal? I know fatigue is a symptom, but the extent of her fatigue seems drastic. I worry that it is mostly a "state of mind" and I wonder if she can pull herself out of it somehow. I think this is my wishful thinking and she is actually much sicker than we all think. Has anyone had this type of experience before? Does anyone have any recommendations? Thank you.