Dog has diarrhea for 3 days straight, what could be the cause?

My dog is 8 years old up to date on shots. We went on vacation and brought her with us (4 hour drive). We got to our hotel put out her potty mats and terrible diarrhea. We changed her mat and 2 hours later same thing. This continues about every 2 to 4 hours for 3 days. Ended up having to find a store to buy more mats since we way under calculated what we would need for our trip. Other then the diarrhea she was completely her hyper normal self and showed no other symptoms. We just got home we are closely monitoring her to make sure she has no other symptoms and is getting better. Any ideas what the cause can be?