Janice Lester

Doctor Janice Lester was a female Human in the 23rd century. 
Early in her career, Lester served in Starfleet alongside James T. Kirk, with whom she presumably had a romantic relationship. She left Starfleet, perceiving a level of sexism in the organization which she believed would prevent her ever obtaining her goal of commanding a starship. 
By 2269 Lester was leading an expedition to the planet Camus II, where she discovered a device capable of transferring a consciousness between bodies. Seeing this as an opportunity, she went about learning the intricacies of Starfleet operations before conspiring with the expedition's physician Arthur Coleman to murder the rest of the expedition, as a means of drawing the USS Enterprise to the planet when they then sent a distress call. 
The ruse worked and a landing party from the Enterprise transported down to investigate. Lester used the alien device to transfer her and Kirk's consciousnesses. Lester successfully played Captain Kirk for a time, but eventually the crew grew suspicious. When Lester made an attempt to kill Kirk in her old body, their consciousnesses transferred back. 
A week later Enterprise transferred Lester into the custody of Starbase 2 where she awaited charges and transfer to Elba II, where Garth of Izar was. 
Later, Kirk described living in the body of a woman as "educational."