Hi there -
My smoothie is similar to Susan's; I don't necessarily use it to keep up weight, but I frequently drink it in the morning just because it's darn good for you. I use frozen mixed berries, plain yogurt (I'd opt for full-fat plain yogurt in your mother's case), a great big handful of packed raw baby spinach, and Naked Juice's Blue Machine. Feel free to sub milk or any gentle (non-acidic) juice in place. The fruit and juice totally mask the spinach and you get plenty of protein, calories, and amazing nutrition all in one glass.
Also, advise having a serious discussion with oncologist about how to keep that nausea in check. Good luck!!
Therefore do not worry about tomorrow, for tomorrow will worry about itself. Matthew 6:34