chicken balance issues

:hmmAnyone know why my chicken Esther always falls forward when wearing a diaper? She then sometimes runs immediately backwards quite fast. I am a little confused...

Hi, I have a barred rock that is 2 years old, had the Marek's vaccine so thinking I can rule that out. In just one day she can not keep her balance when she walks and wobbles slightly while standing. Her feet checked out fine and all the blogs and internet search comes up as possible worms or...