do you have a mill near you? I believe even TSC carries whole oats. Feed Mill and Feed store are both worth a google search in your area. Farm and Fleet, Tractor Supply, Southern States t name a few businesses to look for.
i wouldnt use liquid calcium since ganders dont need the extra and it can cause more harm than good.
Your goose may enjoy whole grains, you will need to experiment with the types and see what she likes. Look into fodder and fermenting as well, both would benefit a picky eater. Geese dont like...