Hi Helen,
I understand your concern, you want what is best for your mother, at the same time you don't want to lose her. It's a really tough call in deciding whether to go ahead with treatment. My mother who passed from PC in 2009, was not interested in conventional chemo after seeing what my father went through with chemo/radiation for his colon cancer in 1988. If she couldn't have the surgery, then she was ready to let nature take it's course. However, as she was diagnosed with stage IV PC with several mets with several complications, she was not going to be a suitable candidate for either surgery or chemo.
Not knowing much of anything about this particular disease, I can't say whether treatment would work well enough to shrink her tumors. What I can say is that each patient with cancer is unique and what works for one person, may not work for another. I think your mom is making a wise choice for her in choosing quality of life which I am assuming must be pretty good right now.
There are many things that she can take to support her system in boosting immunity and helping to manage the effects of the cancer. One therapy I would suggest as a possible alternative that might benefit her as far as managing the effects of the cancer, and who knows maybe even going so far as playing a part in shrinking her tumors, would be to consider receiving IV Vitamin C therapy. There has been much research and success stories of patients who have received IV Vitamin C with positive results. You can read more about this through the links below :
http://www.cmaj.ca/cgi/content/full/174/7/937
http://www.vitamincfoundation.org/
There are also many who have talked about Vit C therapy at this message board which you can search out using IV Vitamin C as your keywords.
I wish both you and your mom, much strength and courage on this journey and that she can know many more days of peace and comfort.