Maybe try putting a bowl of feed out near where you last saw her. Keep putting food out for a week or so and if she has found it, she will realize it's an easy source of food rather than foraging. After a while, gradually move the food closer to the coop. If you have places that are under cover (brush is good) to place the food, she will be more willing to eat there. Hopefully this will at least keep her around long enough for you to gain her trust. She may even realize the other hens have a nice cozy roost to sleep on at night and just join them there. They are flock animals so they don't prefer to be alone...
One other option, although it might be a little frightening for the chicken, is a havahart animal trap. I forgot that I had one set (usually only set them at night) and one of my hens went in, in the morning, to check it out and got "caught". You would have to check it really frequently because if she goes in there, she would be vulnerable to predators, like raccoons, sticking their paws in to get her. I would use this as a last resort though.
