Sounds like you are doing everything you can. What are you feeding? I know some readers will cringe, but sometimes you can add some supplement to their water. Certain times of the year, when the weather is too hot, too cold, or just in transition, hens won't lay. But if you feel an egg, the hen should be laying. She could just be old. Try some green, leafy veggies like spinach that might get things moving. Is she getting enough light? And remember, chickens are meat eaters. I get organic cat food that has meat as first ingredient, and my hens love it. Digestion is an important factor in laying eggs.