Both Ace and Sunny had issues with their feet where they didn't even want to use them, they would just drag them along, but the more they were without perches the more they started using them. Let her out to play with the other guys occasionally and she'll want to keep up and she'll learn to use it again. It's a process. You could even do exercises with her a few times a day, stretching her foot flat and holding it, or setting her on a flat surface like that. And if worse comes to worse and she doesn't get use back she'll learn to compensate by using her beak and her wing to help herself along. Put some platforms in the cage for her to use, put food and water, and some toys at her level. She can still have a good life despite her injury.
