I have one that is always hungry too. It doesn't matter what I feed her and I'm pretty confident it's not due to a lack of proper nutrition. The type food you are feeding is not ALWAYS the source of a problem. However, I would look into changing her diet a bit to see if it has an effect on the problem if for no other reason.
I think mine just doesn't want the others to have any food.
She has literally made herself sick eating before, but never did it when she was the only dog in the house.