With any drug I would wait at least 2 weeks before eating the eggs..Also I would run Acified Copper Sulfate at 1/4 teaspoon per gallon of water for three days every month as a preventive, Canker is somewhat of a carrier disease...
Your hen has Canker. One 250mg Metronidazole tablet per day orally or disolved in the amount of water she will drink in a day and she should clear up in about 5 to 7 days....