It might be sprained or just very bruised and swollen. She may do well just holding the foot up to get around, but here is a good splinting technique on a sprained or broken foot:
https://www.backyardchickens.com/threads/made-splint-for-chickens-broken-foot.1142600/
https://www.backyardchickens.com/threads/made-splint-for-chickens-broken-foot.1142600/