It is likely canker...I had a hen with it....the drug of choice is metronidazole...1/8th of a 250g tablet for standard size. It may not work since it's been so long..canker can spread to internal organs and they eventually die of organ failure or complete blockage of the esophagus. You can also swab betadine into her mouth where you can see the clumps...that will kill it in that location and you can actually see the results within a few days. swab 2x per day. good luck
