Need help figuring out whats going on here

I posted a few months back about this girl here: https://www.reddit.com/r/chickens/s/GnjPwFb9Nb

and I just cant figure out whats going on with her. She walks with her back end low to the ground, but otherwise gets along and gets around just fine.

It's nothing contagious because my 40 other chickens are perfectly fine. I thought it was heart failure and attempted to drain her belly with no luck. Im at a loss here, any clues?