Hi Robin,
My father also has lung cancer too. As soon as we heard this, we have been giving him drinks with whey powder in it...to help him regain some of the weight he had loss. It's been a long process but he has gained back about 5 pounds in 2 months. We give him the whey powder drink twice a day and include Berry Green - which contain organic fruits and vegetables; Perfect Food - this has wheatgrass in it; CoQ10; Vitamin C powder and a teaspoon of cod liver oil. So in essence, this is a very powerful drink with a high nutritional value. On top of all that, we juice fresh veggies and fruit daily for him; give him essiac tea twice a day; eliminate ALL sugar from his diet (apparently cancer cells love sugar); and red meat.
A few weeks ago, we started to try something that is called Transfer Factor (from 4life) and it seems to have given him more energy (these are capsules that help build your immune system)...perhaps, you should do some research on these products and decide whether any of this can help your sister.
Take care.