Hello and welcome to BYC! Glad you joined.
Rita won't just set eggs. She has to be broody to want to do that.
If you are going to be keeping her, you will need to build a coop and good sized run.
Once they are built, you can move Rita into her new home and get 3 chicks and raise them in a protected area where Rita can see them while they grow. Once they are about 4-5 weeks old, you can fashion a chick sized door and release them from their brooder space. They can run back into the brooder if need be but Rita wouldn't be able to get in there. I have found this to be an excellent way to easily integrate youngsters into a flock. It should work equally well in a flock of one.
Hi, glad Rita has found a caring home with you. If you ever need medical advice for her, you can find it on this forum: Emergencies/ Diseases/ Injuries/ Cures
Hi! I'm happy to read Rita's survivor story. I hope you will keep us posted with how she is doing and the expansion of her family. She is lucky to have you.
Thanks for joining and welcome to BackYard Chickens!