I have a chicken that is around 3 months of age. The other day I noticed her limping a little and checked her over and didn't see anything wrong with her. Yesterday, she was walking fine so I assumed she was ok again. Today, I go up to check on them and she is holding her leg completely off the ground and limping around on one leg. I looked at her foot and leg and don't see anything abnormal. What could be wrong with her?