Penguin posture but NO OTHER SYMPTOMS

[Homesteadchickychick]

For over a week now, my 5 month old black australorp has been waddling like a penguin and standing straight up with her tail touching the ground most of the time. I took her to the vet on Monday 2/26...she was not egg bound, was negative for worms, but did display some mouth breathing while at the vet and on/off the rest of that day. No cough/discharge/wheezing/lameness, etc. They said she maybe had some mild inflammation to the left ovary, but otherwise seemed like a healthy bird upon assessment. She has consistently been eating/drinking/poooping like normal, and did just start laying eggs on Tuesday 2/27. She has laid 2 eggs total so far and both looked completely normal in size/shape/shell. No one else in my 20 bird flock are acting different. I have isolated her in a dog crate in my house since Monday after the vet with no change in behavior. She is very vocal and wants to be back out with her flock, but I fear the roosters will peck on her and mate often and further bother whatever is going on.
I have talked to a few of my friends with chickens and no one has experienced this --- pleaseeee help.

What is going on and what do I do with her???

I had a chicken stand like this, it was after an attack and she had wry neck. I fed her eggs, and rooster booster. She did improve