I think you are over-reacting a little. Unless you got a "Cold hardy" chicken, then it will be ok. Just make sure it has shade, water, and ventilation.
I grew up in South Mississippi, about 35 miles north of the gulf. Its hot. The temperature does normally not go above 98 or so. However the air is so humid that sweat does not evaporate, therefore sweating doesn't cool you down. In dryer climates like you are in it will.
The reason I say this is that them panting in your 100+ days, will cool your chickens down more then ours did on 98 degree days. Its harder to stay cool where I grew up.
We never lost chickens due to the heat. We had Rhode Island Reds, and domineckers
(Dominique).
Just give them plenty of water, ventilation and shade. They should be fine. Chickens are much more hardy then we give them credit for. After all, to my understanding most came from Asia/India, that's a hot place. Your girls will be fine.