You need to discuss with your doctors asap a major pallative treatment plan if your Mom persists in deciding she wants to die. My doctors were quite explicit about how the tumors would grow and how painful the process would beYou mom will still need a feeding tube and much more than just morphine to get to the end. So read some of the blogs here and posts about people dying. It will be the worst year of your mother's life and yours.
Now I understand your Mom's feelings and my own mother declined any more treatments for her emphysema and lung conditions once the oxygen was not enough. However in her case there was zero possibility of a cure, just prolonging the agony. Your mom has a chance to beat this.
Expect some heated feedback from this group urging you all to reconsider. My doctors gave only a 30% chance of curing my cancer, much less than the 60% chance that your Mom's medical team guesses. They were right in that even after very painful radiation and treatment, my cancer came back and I had to do massive surgery which has stolen my ability to swallow - not even a sip of water or bite of food. I am being told that my cancer will come back again if I don't do more radiation and chemo and even with that, I only have a 50% chance of controlling this cancer BUT I WOULD DO ALL OF IT ALL OVER AGAIN as my wife and son need me.
Just know what you are getting into. I will not sit in judgement of your Mom - it is her choice and my Mom often said how living was not fun anymore - she missed my Dad, my brother, her sisters and brothers, her mom and Dad all who she believed were just waiting in Heaven for her. She even had dreams at the end about their joyous reunion. Please have your doctors sit down with your Mom and walk her through what lies ahead so she does not regret her decision. I know they say right now they cannot answer but if you rephrase the question to: Has any patient ever refused treatment and what happened to them? Or Has the cancer returned to any of your patients and killed them, and how was the last year of their life? you will get more specifics of the possibilities.
Sorry to hear about your Mom
Charm