My 84 year old mother who lives with my wife and myself drinks 2 large vending machine cappachinos, litte water and little food. She is mentally with it, although sometimes confused. She eats mostly sweets. Should I insist she drink more water, limit her capps and insist she eat nutrious food?
Elders lose their taste for most things and meals can sometimes be overwhelming. Try offering several small meals instead, 1/2 sandwiches, small cup od soup instead of a bowl, applesauce cut up fruits and veggies, cheese cubes, etc, readily available. Freeze some yogurt cups, replace candy with dried fruit, nutrition bars, etc.
I would not stress too much over nutrition. Encourage her to eat, make things available, but let it be.
Has she been checked for Diabetes? You say she is with it AND confused? If she is "with it" it's her choice. If she is confused, and especially if diabetic, step in.