Dr. Judy Barnett was a psychiatrist that worked for the CIA. Although she was highly accomplished and had an ivy league education, she came to the CIA because she wanted to serve her country (After Six).
She met with several of their field operatives to discuss the psychology repercussion of their work as well as problems in their personal lives. Her patients included Sydney Bristow, Michael Vaughn, Jack Bristow, Arvin Sloane, and Marcus Dixon. She had a very brief affair with Sloane.
After he learned that Sydney's mother killed his agent father, Vaughn received orders to visit a CIA psychiatrist - Dr. Barnett. Barnett questioned whether his relationship with Sydney was appropriate (The Box, Part 1).
When Jack Bristow learned that Irina was still alive, Arthur Devlin ordered him to speak with Dr. Barnett. She was a shrewd judge of Jack's character; she did not believe that he was being truthful with her or himself and asked to see him once a week (Masquerade).
Sydney meets frequently with Dr. Barnett to discuss her mother (The Enemy Walks In).
Following the death of his wife and at Vaughn's prompting, Dixon saw Dr. Barnett to discuss his excessive violence on the job and his use of painkillers. When Dixon manipulated the results of his drug text, Sydney lied to Dr. Barnett to cover for him (Countdown).