I'm glad Maddie is feeling better!
The live cultures in yogurts help reestablish the base of "good" bacteria in the intestinal system. When you are given a broad-spectrum antibiotic, it kills ALL the bacteria.... good & bad, which leaves you prone to diarrhea & yeast infections.
Main thing with diarrhea.... HYDRATION!! Fluids, pedialyte, whatever they like to drink! If diarrhea lasts over 24 hrs without ANY improvement, consult an MD.