1-year-old chicken can't maintian balance, has twisted foot

My year-old Wyandotte began losing her sense of balance on Sunday. She started tipping forward and back a little and it has progressed to her not being able to walk well at all. She stands up and uses her tail to try to balance and when she flops over, she uses her wings to try to right herself. Her eyes are clear and bright. She doesn't splay her legs or wings out like you see with Mereks disease. She's eating and drinking (although she is losing weight). It's heartbreaking to watch her try to walk. We have her in a large cardboard box right now, keeping her contained so she doesn't hurt herself. Any ideas what might be wrong with her and how to treat her? I've seen some sites say that it could be anything from an inner ear viral infection to something like lymphoma. Any help is appreciated!!!