After a few weeks on the radiation/chemo she won't be able to taste anything, so don't worry about trying to find things she likes. Go for calories and protein.
Boost and Ensure both make "plus" varieties that have about 100 more calories than the standard formula. Try to get 4-5 into her a day and she won't need a tube.
At the worst of the treatment she may only be able to take the vanilla flavor. Even though she can't taste, other flavors may burn her mouth due to the radiation burns. Even chocolate burned my husband's mouth.
Early on though, buy high calorie yogurt, ice cream, protein bars, yogurt shakes etc. Stick with plain flavors, the chemo makes everything taste bad (metal taste). You can grind up soup, but nothing spicy or tomatoe based. Oh and citrus will burn too, even things like melon which you think would be ok.
Good luck and god bless,
Michelle