Is my girl broody or having a serious laying problem?

[canny75]

I have a Barred Rock with a problem. This year-old BR was a great producer until last week. She's now completely stopped laying, yet she won't leave the box unless I lift her out. She does eat and drink when I put her out in the run or let her range. I've given her yogurt and tomatoes to keep her hydrated, too. She and her roommates - all girls - spent the winter under a red heat lamp. so they never took a break from laying.
I've seen no weight gain or discharge from the vent. She IS doing some moulting. My four other girls are fine.
Is this girl becoming egg-bound, or am I seeing some sort of odd, seasonal broodiness? How long does it take for a girl to become egg-bound, and how can I help her if that's the case?

Thanks for your ideas!

 

[loverOFchickens]

Does she make RRRRRRRRRing noises when you lift her out of the nest? Are there fake or real eggs in the nest?

 

[canny75]

She makes normal resistance noises, but is calm when I hold her or palpate her stomach. No eggs - fake or real - in the nest. Thanks!

 

[Happy Chooks]

Does she stay on the nest all night? Where is she "molting"? Broodies will often pull the feathers on their chest out.

 

[M To The Maxx]

Does she look like this when you see her in there or pull her out?

 

[canny75]

She doesn't sit with her wings down. She seems comfortable, alert, and upright. If she weren't on the nest so much, I'd have no concerns at all. The feathers I've found are from her rear, chest, and tail, but she doesn't have that bedraggled look common to molting birds.