If she is already having issues, keep her inside. Yes, extreme change isn;t really good, but 118 is also very much NOT good. In my experience chickens dislike the taste of electrolytes intended for them, and they will avoid drinking the water to which they have been added. Gatorade works just equally well, and they will actually drink it. There are a lot of things that can cause lethargy, b ut the heat is certainly one. Since you only have 4 birds, I would recommend that you bring them ALL inside where it is cooler for the next few days.
My birds have no problem with the Durvet electrolytes I put in their water. I mix it a tad weak though.