When I was going through chemo I could only tolerate foods once and then I would get sick of them, so lots of people made me foods using only veggies and protein in large batches, but I couldn't eat the leftovers because it was kind of "one and done." So I'd just recommend really mild foods (not too much seasoning) and lots of variety. My favorites were actually smoothies, such as spinach, blueberries and almond butter, since they were cool and not too flavorful, and you could just sip them until they were gone. More fruit than I would have normally but when you're doing chemo you have to work with healthy foods to try to get things down.
BTW, realizing that cancer EATS sugar was a huge factor in kicking my butt on over to Primal/Paleo. Good luck to your loved one!
I feed my healthy cells and starve the rest.