Tail down, stiff legs

[Tambo26]

I have a 3 year old (sweet) Buff Orpington hen and these are her symptoms:

-She seems to be a bit stiff in the legs (for the last 3-4 weeks)
-Her tail is up and then it slowly goes down. The "penguin" look. (last 3-4 weeks).
-When she is picking up treats off the ground she SOMETIMES looks like she is having a hard time, she's stiff and her tail almost dragging on the ground, like her legs want to give out.
-She has had a very minor nasal "clicking" (for lack of better explanation) for some time. Occasional sneeze.
-She wants to be laying down a lot.
-She is very skinny.
-She hasn't laid and egg in at least a year. (this is the case with she and one of my other three)
+She eats and drinks well
+Her poops are regular and normal.
+She is interested in treats.
+Her eyes are clear
+Her comb and wattles are healthy and red
+She's talkative.
+Her crop was full last night and empty this morning.
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I see no evidence of mites. I am going to proactively treat for scaley leg with a wash and vaseline even though I don't think that is the case.
Egg peritonitis? I've seen no yolky discharge.... still possible? No eggs laid in at least a year.
Mareks? Please, no.
I wormed them all 6 months ago. Probably should again now but I'm worried that she is possibly in need of an antibiotic.... the wheezing? Maybe an infection? (there is no bad smell though) Respiratory infection?
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I've been putting out a simple mash so that I'm sure she's getting all the nutrients from the chicken food plus extra water. I've been putting the Chick Saver (chicken gatorade) in their water ever 3 days or so.
I've been giving her 1cc of B12 every day.
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First thing in the morning she is spunky and up and at it. Then quickly it is like her legs get tired or something and she just wants to lay down. She's not overly sleepy.... Doesn't seem to be in pain but I guess its hard to know with chickens.
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I'm just wondering if anyone has any thoughts.... ideas. I would do an antibiotic and or worm again but I'm feeling like..... I don't know if EITHER is needed.... or both are needed..... If I do both could that possibly overwhelm her little system.... I need to see if the local vet knows anything about chickens.
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So... thoughts, suggestions appreciated!
Thanks! (and sorry for the wicked long post!)

 

[Tambo26]

10 months later and leg stiffness is still the same. No worse, no better. I bring her inside and feed her softened feed two or three times per day. She is still hungry and bright eyed and feathers are gorgeous. She's even put on a little weight. She's very talkative and is enjoying the attention. She loves being held. Just wish I knew what this is!

 

[Eggcessive]

Since she has not laid eggs in a long time, I would suspect that she is an internal layer, or have egg yolk peritonitis. It can cause a stiff gait that looks upright like a penguin. She obviously was suffering from a respiratory infection when you first posted. Most respiratory diseases in chickens are chronic, and can come back whenever there is stress. Mycoplasma (MG, MS) can cause respiratory symptoms, and MS can affect the joints, causing swelling and stiffness.

 

[dolcebluesea]

10 months later and leg stiffness is still the same. No worse, no better. I bring her inside and feed her softened feed two or three times per day. She is still hungry and bright eyed and feathers are gorgeous. She's even put on a little weight. She's very talkative and is enjoying the attention. She loves being held. Just wish I knew what this is!

Did you ever find out what this was? Realize it’s an old post but I have a 4 year old Australorp with the exact same symptoms except Poppy is still laying a few eggs/week.
She’s been like this for five months. Brought her to two vets that put her on antibiotics at the onset but while there’s improvement, she’s still walking little with stiff legs, tail down, slightly wheezy breathing and the occasional sneeze.