My hen in walking strange?

Okay so I have checked all my books on chicken health to try and find what's wrong with my two year old hen, Easter. I thought maybe she was egg bound, but she does not show all those characteristics, but then I thought it might be egg peritonitis. Easter has been walking like a "zombie", she stomps and moves very slowly, almost like her legs do not bend. She seems unable to run, even when I go outside to give the chickens treats, and has not roosted in three nights. Instead she sleeps in the nesting box. She is eating just fine. When she walks, it appears her bottom is so low to the ground that she is sitting. Most of the time her tail feather are droopy. A few weeks ago she had mild sour crop, which I did my best to cure myself(i am only 15). I appreciate any help you can offer on this topic. Thanks!