Tylosin is actually one of the few drugs you can get. Jedds and this one usually have it, but Jedds is temporarily out:
https://pigeonsuppliesplus.com/products/tylosin-99-100-grams-pdr-pigeon-supplies-plus-line
Dosage is 1 tsp per gallon of water (always add water to the powder to mix properly)...
You might have seen some feed inside the beak or pus, even. Has she had any sneeze or rattles when breathing? If she has tumors, it could be from a poultry virus. I would get a necropsy through your state vet if you lose her. I probably would also treat her with Tylosin, just in case of MG, a...
I would be concerned that your chicken might have tumors, since there has not been any pus expressed from the eye area. Can you take a picture of the canker inside the beak? Would it be possible to see a farm vet for advice?