Unfortunately at this age, Mareks disease might be a possibility. Hopefully not, but an injury. Keep her close to food and water in her own pen, but close to her flock. Can you insert a finger just inside her vent 1-2 inches to feel for a stuck first egg? I don’t anything on the footpad that she make her lame. Here is some reading about Mareks disease to learn about symptoms:
https://extension.umd.edu/sites/ext...Preventing Mareks Disease in Small Flocks.pdf
https://www.backyardchickens.com/articles/the-great-big-giant-mareks-disease-faq.66077/
https://extension.umd.edu/sites/ext...Preventing Mareks Disease in Small Flocks.pdf
https://www.backyardchickens.com/articles/the-great-big-giant-mareks-disease-faq.66077/