(written from a Production point of view)
Leslie Carol Shatner (born 31 August 1958; age 59) played an Only girl in the Star Trek: The Original Series episode "Miri". She is the eldest daughter of actor William Shatner, and sister of Melanie and middle daughter Lisabeth Shatner.
Young Shatner, together with her younger sister Lisabeth, shot their scenes from 25 August through 26 August, with an additional day on 29 August 1966, under the supervision of a social worker. (These Are the Voyages: TOS Season One, 2013, p. 258) For the shoot, Leslie took her younger sister under her wings as the latter, then five-year old, recalled in Captain's Log: William Shatner's Personal Account of the Making of Star Trek V: The Final Frontier, "Leslie accompanied me to the makeup room to visit dad. When we walked into the room, he was sitting in the make-up chair, his back to us. We ran forward, excitedly, relieved to see his familiar outline. When he turned towards us, I caught a glimpse of his arm and saw the skin on the inside of his elbow was covered with a long, bluish red scab! I blanched, and my dad burst out laughing, and told us to touch the sore. It was made of rubber. At that moment, I realized everything was "pretend". Once I understood, I relaxed."
Lieutenant Leslie, played by actor Eddie Paskey, was named for her as he himself indicated on his personal website, "But, how did he get the name "Lt. Leslie"? This was a result of his friendship with William Shatner. During a scene in which Eddie was at the helm, Bill felt that he should have a name since he was to issue a command to Eddie. Thus, he became "Mr. Leslie" named after Shatner's oldest Daughter, Leslie!"
The Star Trek Encyclopedia incorrectly lists Leslie's younger sister Melanie as the "girl in the black lace dress" in TOS: "Miri", however, that girl is actually not one of Shatner's daughters and Melanie wasn't in "Miri" because she was only two years old at the time.