K.J.
Yes, there is a very nasty virus going around, I am a midwife and I was taking care of a baby post-partum for a family and the baby got this virus and had diarrhea for 2 weeks, we were all very concerned but it did turn around. All the advice you have gotten here has been good, especially the BRAT diet (bananas, rice, applesauce, toast). Keep your granddaughter's bottom coated with diaper cream and as clean as possible, also make sure she is hydrated. If she is still breastfeeding that's best, but if not try pedialite or another electrolyte balanced drink or popcicle. Take care and good luck!
-K.