We've now lost (well, put out of their misery) 2 hens to identical symptoms. Both started out with purple-red combs and started getting yellow smelly discharge. Not egg bound, but after a couple of days started adopting a wide legged stance and lowered tail.
They have gone with maybe 6 weeks between them. Both ex commercial (although free range) and approaching 3 years old. The first was laying fart eggs before she appeared unwell which made me think egg (or yolk) related peritonitis, but the second hasn't been laying for about 4 or 5 months. Starting to worry we may have some kind of infection in the coop... or could it just be bad luck and egg related??