There's also a lot of things that simply go wrong and there's nothing we can really do about it. We can only make do. If she's having trouble absorbing nutrients, there has to be a diet change.
Since my mom can't eat raw vegetables in their natural state, she got herself a Vitamix blender so she can have a bunch of them at once in a breakfast smoothie. Still not very high-calorie and she still doesn't eat enough, but at least they could get their fill of veggies and fruit all at once and then eat other things during the day. And you could always add protein shake mix to that. I sometimes have trouble digesting dairy and fats myself, but protein has never been a problem. When I was recovering from stomach flu, the only things I COULD eat were apples and sushi.