Hen with candida or canker?

[colt_brookstone]

1st pic is of her during her better days and the 2nd when it’s worse.

Currently have a bantam delaware hen. She’s currently almost 10 years old and for the past 3-4 years, she has had this yellow curd developing in her throat.
I would give her fishzole (metronidazole) tablets and it’d go away. However, it would continue returning back and in the past year or so she has gotten worse. It’s to the point where we have a soft toothbrush that we use to brush her throat with iodine and loosen it.
Again, has to be done weekly.

She occasionally develops a sunken face, excess drool (not much), gurgling noises (usually bc of the stuff in throat that comes back).

Medications I’ve tried are:
Fishzole tablets
Metronidazole 20% avian canker for birds (powder)
Medistatin
Etc.

Currently trying acidified copper sulfate to destroy both good and bad bacteria in the throat x 10 days and a probios powder for afterwards.