Where was the tumor she had? Is it still there, and have you had any others with unexplained tumors? Some tumors in chickens can be related to 2 different viruses, although there are others that are just spontaneous. Will you have a necropsy by the state vet lab on her if you lose her? Testing...
Is there any way you can see a vet or farm vet to let them take a sample of the yellow material to test it? It looks like canker, a protozoan infection, but canker smells bad. Wet or diptheritic pox from mosquitoes in hot weather also can look the same way with yellow plaques. The latter is a...