Has she had the Big D for more than a few days? If so, I would schedule an appointment with the vet.

As for the food issue, you should withhold food for 24 hours, but ALWAYS leave a water source. You might even want to give her a little chicken broth to entice her to drink more. Your primary concern for now is to keep her hydrated. I would also give her two teaspoons of Pepto Bismol. Chances are she just ate something different and her stomach flora isn't used to it, but a visit with the vet wouldn't hurt. Better safe than sorry