My very dear friend had a prognosis of eighteen months, but she lived for three years. During the last few months, she felt the treatment was worse than the illness and stopped the treatment.
I think that, in the end, it was too much for her to cope with, for no real benefit. She made the decision to stop any further intervention, including an experimental new medication. We had to respect her wishes; she had gone through some unpleasant treatment and had come to terms with the outcome.
I think all you can do is to support your friend,particularly if others are advising otherwise. I had some conversations with my friend, in which we spoke of very meaningful (to us) things. We also spoke of how much our friendship had meant to each of us. I saw her last in the hospice, a few days before she died. She recognised me and it was the
hardest thing to do, but I was glad I was able to say goodbye.