Sarah, you might also try plain yogurt before switching her food. Have your parents pick some up the next time the go to the grocery. Just plain yogurt. But a couple Tablespoons on her food. Might help. That is what they have to do with greyhounds b/c they have such horrible gas.
Or even an Acidophilus supplement which is one of the "good" microorganisms found in yogurt.

Yogurt my be easier to find some parts of the country than a supplement, but, you can order it online.

I use Vet Basis Healthy Breath and Body, because it contains more than one "good" microorganism.