Greta Simsis Fletcher Stone's oldest friend and editor in the Season 2 episode Failure to Communicate. She was portrayed by actress Mimi Kennedy.
Greta knows much more about Fletcher than his wife Elizabeth. As such, she provides the doctors with much needed background about his medical history, particularly his history of drug and alcohol use.
She also provides reassurance to Fletcher when his wife leaves him after he is diagnosed with malaria because Elizabeth realized that Fletcher had been lying to her.