One other thing. No competant vet prescribes painkillers for a hen that can't walk until they know why. If it is a dislocation, or joint related then having less pain just encourages the hen to walk and this can just cause further damage.
The pain is there in part to dicourage one from using the...
I'm not stating that it is either of these, but that looks like a possible dislocation, or osteoperosis.
Have you tried Calcium Citrate?
Did your vet check for a dislocation?