It is a very difficult time for your family. I understand both
parties reasoning and I am sur both care about her. However; your mother and siter don't want to see her going through pain and agnoy but at the same you thinking about her long term surrvival. Your approach is pragmatic and I support it.
I am giving you a true example. My best friend was diagnosed with multiple myleloma in 1997 and he is just doing fine. He had two bone marrow and many years of chemo and radiation. The 6-7 year treatment a tough ordeal but the end result iis that he got back his life.
His cancer has been in remission for the past five years and he does not take any medication or chemo or radiation. He is just enjoying his life.
My thoughts and prayers are with your family. I am hoping and praying that your family can make a decision that is best for your sister.
God Bless you all.
WS