Mother, 80 years old, @ 95 lbs. Having Esophagectomy

My mother, 80 years old, 5' 3" who was 110 lbs. prior to her diagnosis and is now at a stabilized weight of 95 lbs. post-radiation and chemotherapy, will continue to see her weight go down and would result in more complications. I've been going through the support group and have seen that everyone has lost weight, how concerned should I be that after surgery she will lose additional weight. She is strong and my father has been wonderful; but I worry about her losing weight and not having enough energy to keep active. We aren't getting a lot of details post-surgery, other than, it will be life changing.