Joanna McCoy had attended school on the planet Cerberus. She was there in 2259 when Cerberus experienced a crop failure and the entire population was in jeopardy of starvation; fortunately, they were saved by Carter Winston's philanthropy.
Joanna was created as the result of a conversation between D.C. Fontana and DeForest Kelley between the first and second seasons of The Original Series. Fontana proposed that McCoy could have an estranged son, to which Kelley replied that he thought the doctor should instead have a daughter. Consequently Joanna was added to the series bible. (Writer's Notebook: D.C. Fontana, TOS Season 2 DVD special features)
In The Making of Star Trek by Stephen E. Whitfield and Gene Roddenberry, which was written before the original series' third season had aired, Gene Roddenberry is quoted as saying "In a future story we will bring McCoy's daughter Joanna aboard. She will be a lovely girl, and Captain Kirk, of course, is going to be involved with her. Dr. McCoy is suddenly going to discover he is a father viewing Kirk from a father's perspective. An interesting and sometimes angry new McCoy-Kirk relationship will be seen."
In the original draft of "The Way to Eden", the character of Irina Galliulin was originally written to be Joanna McCoy, and to be a love interest for Captain Kirk (the episode's original title was "Joanna"), but that script was ultimately rejected.
The Star Trek Concordance by Bjo Trimble adds to Joanna's biography, stating that she was twenty years old (born c. 2249) and was in training to become a nurse; and that although they write each other often, Dr. McCoy's duties aboard the USS Enterprise kept the two apart.
Star Trek II: Biographies gives her full name as Joanna Lee McCoy.
In the Star Trek: Myriad Universes story A Less Perfect Union, in an alternate timeline, Joanna's mother dies a month after her birth and she is raised by Leonard as a single father, bringing them closer together.
Joanna plays a large role in the Star Trek: Legacies novels Best Defense and Purgatory's Key. She is sent to the Jatohr (β)'s universe via the Transfer key (β) along with Ambassador Sarek, then-Councilor Gorkon, and others.