Thank you for the update!
Ih ope that with time and patience you will be able to cure her of this nasty parasite. It is not easy and I love your dedication.
Yes, to me it looks advanced but a prompt treatment with metronidazole or similar will show if she can get rid of the flagellated protozoa and be restored to full health.
Some soft nutrient rich feed like scrambled eggs with grated carrots, millet, rolled oats and sunflower oil will help to...
Yes, thank you!
It does look like canker (trichomonosis) to me which can be rather hard and not easy to pry off.
Do you have doves or pidgeons around?
https://www.msdvetmanual.com/poultry/trichomonosis/trichomonosis