I have not read thoroughly through that thread, just my two cents:
Me, wanting to do the ducks a favor once used self-harvested hay in their house during the height of winter. They really liked it, until it all got wet and became moldy. Really, really moldy! I had to wear a mask while removing it from the duck-house and despite protecting me i was coughing my lungs out for the next couple of days…
How was the aspergillosis diagnosed? - A vet our just you drawing the conclusion?
After my hay incident, i went to my doctor - also thinking of aspergillosis - and was told that it is very rare. Contrary to the common believe, aspergillus is not black mold, aspergillus fungii are either green or transparent and they only grow in starch-rich environments (like bread!). Aspergillus simply cannot survive in straw. - Other fungii do, but they won't be able to survive in animal-lungs. Fungal lung-infections of poultry are very rare and unfortunately very deadly, wiping out the whole population of shoebox-chickens in egg-"farms" within hours…
Looked up Oxine AH and what i found is that this is a solution of Chlorine-Dioxide in water [
https://www.heartlandvetsupply.com/p-5139-oxine-ah-disinfectant.aspx ]. Who told you to make your duck
inhale this?
The standard application of Chlorine-Dioxide is as a disinfectant for drinking water and to remove bio-films, there was no reference for any benefit of inhaling that stuff, on the contrary:
https://en.wikipedia.org/wiki/Chlorine_dioxide#Safety_issues_in_water_and_supplements
What if you pause with her inhalations and see how plenty of fresh air works out for Poppy? - Her lungs might have been irritated
My doctor told me, that there is a situation, called »Farmer's Lung« which is a reaction against the pathogens in moldy straw, hay or similar materials that can turn chronic.
https://nasdonline.org/41/d001609/farmer-039-s-lung.html
Treatment for this condition as described on the web-site above: »…avoid further contact with moldy dust.« And »…bed rest is recommended and oxygen therapy…«.
You already did the right thing and removed the moldy stuff, now start with the Oxygen therapy and let her breathe in fresh air. As many asthma sufferers can tell you
cold air is best to soothe down an asthma flareup, so it is the right time for Poppy to go outside.
Just my 2 cents…