Well what we do here (but it's only maybe 105 today) and my littlest ones are already 10 weeks, is give them shade.
And I run a fan into the coop only so that when the hens are stuck on the nest box they can breathe some. It was 102 inside there yesterday even with the fan, but these girls are laying age already.
Is there ventilation in the shed? You may have to move them out of there if it's hotter inside the shed than out in the open air. Leave the door open as you're already doing and run a fan pulling cooler air through there but without blowing right on them? I honestly am struggling with an answer because this seems to be a very difficult situation.
Some people freeze old water bottles full of water and then lay them around. If the chicks have room to move closer or further away from the coolness, it may be an option.
Keep the direct sun off however you can with a tarp or a tree or something.
I run water into the run at least once a day so that they can walk around in it and cool down. They cool down at least partially through their feet. Maybe you can cool Mama hen down.
Hopefully you can keep it down to maybe 100 degrees for the first few weeks until they can move around and cool off some?
