Someone else had a chicken with a very similar-looking lesion on the bottom of the beak. I agree with @azygous that I would just watch it and not do anything invasive. If you should lose her someday, and can contact the state vet for a necropsy, they probably would be able to diagnose what the lesion is. Here is a list of state vets:
https://www.metzerfarms.com/PoultryLabs.cfm
https://www.metzerfarms.com/PoultryLabs.cfm
