I've got an 8 year old Barred Rock and other than having arthritic legs, she's still going strong! I've heard of people who have chickens who are 10+, so it could be that Eddie12109's girl is reaching the end of her life, but it wouldn't hurt to spot check for other potential issues :wee .
Oh no. Poor girl! Have you checked her crop? It should be empty in the morning, and full at night (if she's been eating enough). If it's swollen and squishy like a water balloon, it is probably sour crop. If it feels more like a hard mass, then she might have impacted crop.
For sour crop...