Foaming in the mouth

Pebbles gave me a good scare today. It was a very nice hot day out. I took her out for a run and she seemed a bit tired today. All of a sudden the leash yanked me back, I turned around and saw her plopped down on the soil under a shaded area by the sidewalk bushes haha. It was too nice of a day to head back home so the next stop is the Dog Park. So many dogs out today and a few cute puppies! The Moo cow looking dog is back! Then I noticed her mouth was foaming. This is the first time it's ever happened. The lady on the bench noticed and asked if she was ok and had her rabies vaccine. I said yes and not sure what was going on. So I took her home. As soon as we got in the car she was fine. So got home and look up online to see what it could be and phew it's just her dehydrated. She looks normal now and running around like a puppy!