How old is she?
The beak looks like NBD to me. The little spot on the comb looks minor too. Her comb and wattles are vibrant so she looks okay to me.
I have some molting already so it's possible she's starting to hormonally shift into the molt phase and stopping egg production. But if she's your only one left then yeah, she's probably pretty lonely unless she was a loner to begin with.
How do you know one had a tumor? Necropsy?
A lot (not all) of my egg laying/reproductive issues diminished after switching to soy free feed. I do corn free now as well and supplement with a lot of mealworms, sunflower chips, and sardines, but yeah...$$$.