It does not look like fowl pox to me. How long has that lesion been there? Does her beak smell bad? Can you get another pair of hands, and look into her beak and throat to see if there is any yellow gunk inside? Canker (also called trich) is a contagious protozoan disease carried by pigeons, and smells bad, and is seen in the picture below. It can interfere with eating, and can spread into the esophagus and crop. Occasionally cancer can look like this as well. Canker is usually treated with Fish Zole (metronidazole, Flagyl,) which you can find online. Dosage is 250 mg daily given orally for 5-7 days. A vet would be best to get a proper diagnosis if one is available. Here is some reading about canker:
http://www.poultrydvm.com/condition/canker
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