HI I just wanted to clarify some things I see in this post and hope to help.
First, if the bird was acting ill in July - it's not botulism. They'd have died. Likely this is an ongoing "something" that is finally culminating to the point where the bird was weak and thus unable to fight anymore.
As for vitamin E, higher levels of vitamin E supplementation can be toxic, yes - but you can give up to 700 IU daily to an average sized hen for a week without issues. Most capsules are around 400 IU.
I suspect what has happened is that somewhere along the line this hen's bacterial balance has gone out of whack leading to bacterial and possibly Candidiasis issues. That would explain a number of things. I haven' thad a chance to read the entire thread (and will go back). Her droppings look quite mucous which again would indicate a lack of digestive tract health. If she were a younger hen, and this would have been acute (quick and strong) I'd suspect coccidiosis as one of the possibilities. But in this case I don't.
Because of the intense smell of the droppings, a flush is in order for this hen to clear the tract of accumulated mucus, pathogenic bacteria, possible any fungi (transformed yeast that are now pathogenic), undigested food matter, etc in the digestive tract. It should be a medium-strong flush. Long-term yeast/fungal infections (I'll just refer to them as fungal even though "yeast" is the common term from here out, fungal is the form they take at this point) can cause neurological issues. Actually giving her the vitamin E might not have caused a dramatic turn around (because you were treating a symptom, not the cause) but likely kept her from deteriorating worse or dying IF it's fungal.
If she were mine, I'd do this (even if you've done any of this before):
A one-time treatment of a medium-strength flush mash. Simultaneous probiotic treatment, etc.
Continued probiotic, anti-yeast, and vitamin therapy and overall immune stimulation for two weeks.
A good look at her physical condition with 'tweaking' of the diet to encourage increased growth/plumage.
The mash:
1/8th teaspoon of molasses.
1 teaspoon of honey
1 teaspoon of very very hot water.
Mix the above three ingredients. To them, add:
1 teaspoon of yogurt (plain, or "Activia" - best choice)
1 teaspoon of applesauce
4 drops of polyvisol vitamins (if you have them)
a pinch of turmeric spice (if you have it - if not, consider getting some from the grocery store).
crumbles (or pellets made into crumbles in the blender) - enough to where initially the mash is like a not-very-moist applesauce.
Stir well and allow to sit for a few minutes til it's semi-moist but not too goopy as most birds dislike that.
Fast her overnight and feed this as her first meal of the day. Use 1 teaspoon of honey, 1 heaping tablespoon of molasses to 1/2 gallon of water as her sole drinking water for four hours.
After the four hours, replace her water with normal. After the mash, allow her to have her regular mash.
The mollasses flushes out the system as I had outlined above. The applesauce's pectin cleanses the digestive system and acts as a "prebiotic" to the live bacteria probiotics - it feeds them, encourages them to colonize. The honey is for taste with slight antibacterial benefits, very slight. The vitamins are to replace any diminished oil-vitamins which are commonly deficient in birds with long time mycotoxin or fungal exposure, or yeast infections. They will also boost immunity, the E acting as help against E. coli as well as neurological boosting. The A increases mucous membrane health, including that of the lining of the digestive tract.
The turmeric has some good anti-inflammatory properties. This hen definitely has an inflamed digestive tract evidenced by the mucus in her droppings. Inflamed digestive tracts are unable to absorb normal nutrients, likely resulting in her poor state and feathering and general lethargy.
The yogurt, of course, will replace good bacteria (Lactobacilli in most brands, both lactobacilli and bifidobacteria in the Activia brand) which are active against yeast that has turned into its pathogenic fungal state. It also of course acts against digestive tract inflammation and pathogenic bacteria through the actions of crowding, enzymes, etc.
After the first day, I'd use that flush mash (without the water treatment) twice weekly for two weeks as long as her droppings remain smelly or for two weeks and then reevaluate, whichever comes first. For water, I would use 1 tablespoon of organic (not regular filtered) apple cider vinegar in her water as her only water. All of your flock can have this, though for a week I would keep her up as she's likely sloughing off bad bacteria in her droppings, which can be infective to other birds.
The pH of the OACV will continuously combat pathogenic fungi and fungal spores, and make an unfriendly environment for pathogenic bacteria (who like a more basic pH). The bit of living bacteria in the unfiltered OACV will compliment the probiotics of the yogurt. It will also keep the water free of biofilm.
I would use a modified mash daily for the two weeks - one containing yogurt and vitamins daily. Make a tiny amount containing 1 teaspoon of yogurt (or the contents of one acidophilis capsule/tablet), a tiny bit of honey, and 5 drops of polyvisol vitamins without iron.
The polyvisol provides the oil vitamins that might be depleted in a good spectrum as well as vitamin B for appetite and vigor. The reason for an oil form is that water forms of vitamins allow the light-sensitive vitamins to degrade easily and honestly I feel that the vitamin package encourages biofilm in the waterers while losing effectiveness (for the vital oil vitamins) quickly. The slight amount of polyvisol is within safe ranges for the more-easily overdosed oil vitamins without being excessive. After two weeks, you will need to taper off - but we'll reevaluate before then if you choose this treatment program.
If she shows any neck issues, I would indeed give the contents of one 400IU vitamin E oil capsule daily on a piece of bread. It doesn't have to be the whole thing but the polyvisol's vitamin E amount isn't enough to really be truly therapeutic. In all honestly, natural Vitamin E is the way to go (and you'd use less) but synthetic vitamin E will certainly help if there is neurological repathing to do to repair any neuro issues. If you like, you can do this as little as three times a week.
This program is designed as an over-all immune building and fungi/pathogenic-bacteria fighting treatment as we don't know the true cause of this illness. Again the stench and mucous quality of the droppings (while not being acute as in coccidiosis) indicate bacterial involvement at the least.
I'm curious whether the hen has any evidence of feathers lost near the vent, urate leakage (or urine leakage), any white or black waxy or powdery marks at all near her vent, inflammation of her vent, any lower abdoment puffiness? What is her actual usual diet? Is your food less than a month old, kept in an air-tight light-proof cool container? Did she, previous to this, just get introduced to free ranging? Does she have granite-grit available daily? Has she ever been exposed to heavy rains (on the ground more so than on her body), soured or wet or old feed (especially those containing any corn), excessively dusty or older scratch feeds, etc? Any algae water, compost piles, decaying vegetation such as leaf piles, wet hay,etc?
I hope my information I've given here can help. I think concentrating the program (particularly because an abbreviated version of it showed improvement) over at least 2 weeks should help - I do hope it does. It's so hard to tell online. But these things literally can take months to build up, and thus take time to fix.
I very much look forward to your thoughts. She's a lovely hen from an obviously well loved flock.
