Trouble with Heat

Maggie and I got to ride at the Trace Trails today in Athens, TX. We had a pleasant ride in spite of the heat, except that Dixie had trouble with the heat. Her heart rate was fine, her temperature was slightly high, but not too bad, but her breathing was out of control. We trotted/cantered a little, but not a lot. We mostly walked. She was eating and drinking well and acted normal, except for the panting. I haven't been able to figure out what the problem was since she didn't seem to actually be hot. She didn't sweat as much as Liberty, but she did sweat. She also got another girth gall from the English saddle Maggie has been using, so it's back to the saddle drawing board. I'm not sure what we will do about The Other Half ride next weekend. Dixie was still panting when she unloaded at home in spite of multiple hosings. She got right off the trailer and started eating. She never had any signs of stress. Her gums weren't injected and her skin didn't tent. She was a little better after a dose of electrolytes, but I am very puzzled.