Sustainable food production with unlimited quantities.  So basically grains, sugar, and a bare minimum of proteins and fat.  Veggies are out because the land/water cost:caloires ratio is way too high.  Grains are probably best, as the calories/acre is huge.  Sugar as well.  Keep a small amount of animal farming for minimum protein and fat requirements.  Wait that's not what she wants.  Lets make cake and cookies sustainable.