Janet and James Kirk were romantically involved in 2261, but the two "called it off" in favor of their respective careers. Janet was eventually stationed on a lonely outpost at Aldebaran III, where she met her colleague and future husband, Theodore. After Theodore died, she received a stargram from Kirk, but otherwise lost touch with him until 2267.
Doctor Wallace was on board the USS Enterprise during its mission to Gamma Hydra IV. She worked with Doctor McCoy to find a cure for the radiation disease causing rapid aging in members of the senior staff, a task made all the more urgent due to the Romulan presence surrounding the Enterprise at the time.
Doctor Wallace, who was not affected by the disease, was McCoy's right hand in attempting to find a cure, which turned out to be adrenaline. They were able to inject the crew, and Kirk was able to escape the Romulans. (TOS: "The Deadly Years")
Background information Edit
Janet Wallace was played by actress Sarah Marshall. She was described in the final draft of the script simply as being in her "late twenties" and described as both "a beauty" and "extremely attractive".
Wallace was a possible candidate for the "little blonde lab technician" Kirk was engaged to for a time though this is never directly indicated, simply Wallace's off-hand reference to the fact that she still chose to get married after she and Kirk had "called it off".
In the first draft of Star Trek II: The Wrath of Khan, Janet Wallace was in charge of Omega System, a weapon of mass destruction. In later drafts, Omega System became the Genesis Device and Wallace was replaced with a new character, Carol Marcus.(citation needed • edit)
According to The Autobiography of James T. Kirk, her maiden name is Janet Lebow.