I would try to get her back with her flock right away, but you probably should gradually reintroduce her inside a wire dog crate with her own food and water. She has been away so long, they will probably attack her. Is it extremely cold outside? The temperature change inside the house might be a problem too. Besides chick feed, all flock feed or Flock Raiser has 20% protein, and can be good for all chickens as long as you put out some crushed oyster shell for the layers.