Nurse Ratched is a character first encountered in season 3, episode 6 "Doc Flew Over the Cuckoo's Nest"
Nurse Ratched worked as a nurse at a clinic for criminally insane.
After the apocalypse, Nurse Ratched decides to stay at the asylum and keep working. She continues with group therapy and medication. She finds first 10K and then Doc, and brings them both to the clinic. With the assistance of some of the other patients, she performes surgery and experiments.