Did she growl at you when you picked her up? She is probably broody. Hens will pluck a "broody patch" on their bellies to get better contact with the eggs to help keep them the correct temperature and humidity for developing and hatching. They will also stay on the nest, only coming off once a day. Do you have access to fertile eggs to put under her?
Well you can try to put her in a crate for a couple days to see if that works. But if she goes straight back to brooding, I doubt that there is anything that will stop her. She'll snap out of it in a couple weeks.