I went to feed store today - got a vitamin/electrolyte supplement. She is sipping it very very slowly. The feed store guy is perplexed, too. He did say that 2-3 years is the max laying potential for a lot of hens, which is disappointing to me, but I have to be realistic: she hasn't laid an egg in probably 5-6 months.
I also got oyster shell (even though their feed should have enough calcium) - I sprinkled some on the ground around her, and she pecked at it a little.
Her walking seems worse today. This morning, she literally fell out of the roosting house, off the ramp. Fortunately, the feeder broke her fall, so it was just a few inches, but it broke my heart to see her. She was scrambling to get out of the roosting house, and lost her footing.
Just now, I watched her walk around - I confined her to the smallest part of the run and let the other hen out to free range. She is taking 4-5 steps, fully upright, not favoring either side, then she just collapses or falls on her face. If she falls on her face, she curls up her claws at the same time. Otherwise, she just sits down abruptly. She will sit there for a minute or so, appearing to gather strength, before trying to walk again. Her tail is up, there is no discharge. I kept moving the bowl of vitamin water to her side, and she would take a sip or two then start roaming again - she is noticeably disturbed by me approaching her, so I'm trying not to do it often.
I have left a message with my vet who specializes in avian and exotics. Not sure when she'll call back, and I'm not particularly wanting to spend a lot of money on her, even though she is a pet. The vet is a friend, though, who might offer free advice, at least