Update: She died today - just a little over 2 years later, and from the heat.
(We also lost 2 other girls - I was stupid, left them in the coop while I was away 24 hours because the neighbor I've repeatedly chicken sat for refused to check on them and let them out. Then again, I buried one of her hens this week because I couldn't bear to see tossed at the bottom of the trash can, especially after a raccoon tore the bottom of the can and pulled what it could out, leaving it half in half out.)
However, she'd been declining recently - she wasn't keeping herself as clean as the others, her abdomen had been swollen for the past month, and she was walking awkwardly - that awkward swayed gait. The last hen I had with abdominal swelling like that also fared badly with weather change (cold, that time). Prior to that, she was externally indistinguishable from the other hens in behavior and level of healthy appearance. In fact, a veternarian neighbor had commented on healthy they looked, foraging in the yard.
Up until I last saw her Friday evening, she'd been happily going about with her friends... so if my stupidity killed her, my not culling her at least added 2 years.