Chicken standing oddly and limping when she walks

I have had light brahmas for a couple years and haven't had many problems but tonight I noticed one of my hens was standing really weird. She's standing straight up and doesn't like to move much. I don't know how to describe how she's standing. She can walk but she's very slow. She still gets in the coop at night but not up on her perch. She's still eating and drinking. I'm really not sure what's wrong with her or what to do for her. Any advice?