Bananas freeze great. I used to cut it in slices and give her a few at a time.. If she did not eat it all I placed it in the fridge. If we did not eat it by that night, I sliced it up and froze it..
With apples, if she did not eat the whole thing, I did the same thing but then tried to make sure my husband and I ate he rest in a green salad or fruit salad. Or place it in a zip lock and serve it with breakfast the next morning.
With the oatmeal consider only giving her about a 1/3 of what you normally serve her. If she eats it all, add a little more. The rest can be frozen and reheated.
Yogurt, serve small amounts at a time.. May only be 2 tablespoons of it.
When I am ill, a large portion does not look appetizing, but a tiny bit at a time I can handle.. Teach her to ask for "More yogurt, please". Your answer, "I like you manners, yes you may"..