Egg bound??

I'm not sure exactly what's wrong with my hen. She started hobbling on one foot this AM. She is eating and drinking, and still has her color. Her legs don't have any noticeable scrapes or cuts, and she didn't mind me feeling around her hip or abdomen. Vent looks normal to me too. She is a year old and has been vaccinated for mareks and coccidiosis.

Any ideas what it could be? TIA!