As a human who has been on prednisone a couple times, I can attest to the fact that it makes me VERY hungry. I'm talking "buy me the whole grocery store worth of food and cook it please" hungry. It does not, however make one's stomach any bigger, so if I cooked, I'd end up making way more food than I could possibly eat.

In your dog's case, just keep low-calorie snacks on hand, like raw carrots for one good example, to avoid a lot of weight gain. The hunger is all illusory, and if you give in to it, people have been known to gain a lot of weight f on it long-term. So low-calorie snacks are the best bet, and don;t let her near the credit card or she'll be ordering truckloads of dogfood!