Could she have been injured by a rooster mating? I would check her vent by inserting a clean finger inside to feel for a stuck egg or mass. You may want to give her some calcium or Tums just in case she is having egg problems. Sometimes being egg bound can cause temporary paralysis. If she continues being lame, you may want to make her a chicken sling chair to get her upright, keep cleaner, and make it easier to reach food and water. Here are some pictures:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/