Mom (82) is diabetic, just started chemo (stage 4 lymphoma) and yells almost daily at her caregiver to go get her candy. Advice?

She has diabetes, hemolytic anemia and newly diagnosed lymphoma. She has always disregarded her diabetes and eaten candy all the way thru. She is now in and out of progressing dementia and has become angrier, uglier and and more routine in yelling at and to her CGiver to go out and get her bags of candy. She doesn't and won't, but what is the best way to address this repeatedly without expending all energy each time? It seems she spends so much time telling her why she can't and shouldn't do it.....

Thank you....