If it was indeed bumblefoot (staph infection of the foot) that your pretty roo suffered from, and your sister's chicken (nearby?) also suffered from it, could it be that the chickens are coming across something that is cutting or worrying their feet? Looks like you are out west: could they be getting into cactus bits, or mesquite thorns, or any other pointy things that might make small cuts in bare feet and open them to infection? I know it can also simply be caused from various types of trauma (like hard landings) in heavy breeds, but it's just a thought ~ hope you don't ever have to go through that again.
Sending best wishes and healing thoughts your way ~