It shouldn't be the heat...maybe Abby is stressed, or maybe the food just isn't agreeing with her. You can give dogs Kaopectate or Pepto, etc. I would give her a few more days with the food and some Kao, and if she still has a problem, I would look at the food.
Kate started having diarrhea again right before we left to go to NY and she didn't have any rawhides this time. The vet diagnosed it as colitis which is inflamation of the colon which can be caused by several things. Including their food. So it acutally made since to me because Kate has never had a real solid solid poo since she has been on RC Boxer. So I switched her to DVP Duck and Potato but she started it at the kennel and I won't be home until Wednesday to see how she is doing.
So it could be that she is allergic to something in her food if she is otherwise acting fine.