I think you're misunderstanding my comment and maybe taking it the wrong way. Bottom line these symptoms could be from multiple causes. You will need information from a necropsy to get a proper diagnosis in this case. These symptoms are just very vague. Could be anything from heat stroke (my first guess) to an unknown neurological disorder that just started showing itself, to a number of diseases. Chickens are usually sick for a few days to even a few weeks before they even show us symptoms most of the time, so there is really no way to even know if this was prolonged- it just a guess because her obvious symptoms were not prolonged.

There is nothing specific to do for the rest of the flock without knowing more, besides watch them closely. You can up their vitamin intake to keep their immune system up, but that isn't a guarantee to help anything really.