Between the starch, high energy, and possibility of mold, why in the heck would you say "corn is okay for horses"?
Corn is a low protein, low nutrient, "Candy" feed for horses. It is NOT good for them. Plain whole oats is a much better choice, if you have to feed a whole grain. They have a decent nutrient content, and are slightly less "starchy". But really, she's already feeding alfalfa pellets, which are good for horses, high nutrient with quality protein, good energy. So, there is no need to feed corn.
But, I agree, it's probably unneccessay with the alfalfa.