Oh sorry just misunderstood. That is interesting from my experience letting your horse roll in dirt Is the best way for them to dry fast especially for the thick haired and skinned horses usually after about 15 to 20 minustes the dirt or mud sucks up the extra moisture and they are quite dry, you just have to brush the mud off though if you want a clean horse, I know it might sound kind of silly but it works well for my horses! Also if your horse dosent roll you can put dirt or mud on yourself, hope this helps!
If she has long hair it's natural to stay wet longer because it traps the moisture. Make sure she isn't continuing to sweat after exercise bacause that can be reason for concern. The best way to solve the issue of excessive sweating is a partisan or full body clip. If you do that be sure to blanket.