do you cup the flashlight with your palm? I cut a piece of foam for around pipe and used black tape around the end of mine
1" foam pipe to LED light
image was posted for helping me from @R2elk here on byc but mine is the exact same now
idk you know sometimes disease or sickness can cause it as well.... I would research it on google a bit and see what you come up with if its just one hen. maybe give her some extra in a snack?