When you suspect a chicken is suffering heat stress or heat stroke, you need to treat for electrolyte imbalance, shock, and hyperthermia, all three.
This should be considered an emergency. Cool the hen down by placing cold compresses under her wings. Lay her on a cool damp towel and provide a fan to create evaporation from the damp towel to further cool her.
Mix an electrolyte solution with sugar to treat the electrolyte imbalance and shock. Or give her Gatoraid. Give this cooled solution each hour until she is behaving normally.
100F temps will kill if chickens have no way to shed excess body heat. You must supply the means for them to do so. You can do this in a number of ways, but it requires concerted effort during a heat wave when you aren't up to snuff yourself.
When the thermometer moves into the 90-100F zone where I live, I provide a big bowl of ice cubes for the chickens to beak around and drink the icy melt water. I have fans set up in the run and coop to move the air around. In the run, I water down the sand to create evaporation which automatically reduces the temperature as much as ten degrees.
Another fun and effective way to cool down chickens is to freeze canned corn or fruit cocktail into a block of ice and let the chickens peck at it all day.
Where do you live? If it's a place that has extended periods of hot weather such as the southern deserts in the US, you might consider up grading your coop to a structure that can be more effectively cooled. My uncle used to have a chicken farm in the California desert in the 50s, and he cooled his chicken barns with evaporative coolers, also known as swamp coolers, an efficient and economical means of air conditioning in non-humid climates.
