SCLC with paraneoplastic syndrome-my sister

My 69-year-old sister just received a definite diagnosis at Mayo Clinic in Florida of SCLC, limited with paraneoplastic syndrome. It is limited. She is scheduled to begin chemo on Tuesday. Radiation will begin in 3-6 weeks. After 12 weeks of this treatment, prophylactic cranial radiation. The neurologic symptoms led to the diagnosis. At this point in time, that is what is compromising her quality of life significantly and it is progressing daily. Within 2 months she has gone from a vital independent woman to one who cannot lift a spoon to her mouth, stand without collapsing, slurred speech and cognitive issues. We have been told that the treatment "might" improve these symptoms. Has anyone experienced something similar?We have talked in the past when she was well about quality versus quantity of life. Then, she was clear that she did not want to suffer through heroic treatment that have horrible side effects and little hope. Now, I can't read her. I have read some of your posts and see that many feel grateful for life after treatment. But with 10% chance of living only to face suffering...How have you built support for your selves or your loved ones? The doctors are very focussed on the science of fixing the cancer, not quality of life.