Deerchaser, please do not take this a being rude. I'd say not to dart her. There is so many things that go into sedating and moving a deer, and yes this heat is one. Soaking a deer in water is okay for temp control, but by far not the most productive, core temps are what count. I darted one the other day in s. texas at 1pm and 91* outside with no problems. I don't recommend this, but it had to be done given the situation.
If you are good at darting and know what you are doing. Wait till the temps fall well below 75* and do NOT run the deer at all before making you shot.