Since you've got a call into the vet, I would just keep a close eye on her. I went through this exact thing yesterday with my 2 year old draft cross (who happens to be black). It was hot outside and he was laying a lot more than is typical for him. Because I was starting to worry, I got him up and could tell right away he was slightly colicky. Checked his temp and it was elevated but he had good CRT and gut sounds. His breathing was a bit fast so I led him over to where the hose was in the tank and spent about 10 minutes really rinsing him off with the cold water.
By the time I got done, he had pooped once and was acting like he felt a lot better; his temp was down, his breathing was slower, and he ended up feeling good enough to take off at a run after his buddy.
I second what Speed said, since you've already contacted the vet, just keep a close eye on her to make sure she doesn't start rolling violently or thrashing. Plus, if it's above 90* where you are, it couldn't possibly hurt to rinse her off a bit.