(written from a Production point of view)
Darleen Anita Roddenberry-Bacha (4 April 1948 – 29 October 1995; age 47) portrayed a blonde girl in the Star Trek: The Original Series first season episode "Miri". She received no credit for her appearance and was brought into the episode by her father, Star Trek creator Gene Roddenberry.
Young Darleen, with her younger sister Dawn, shot her 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)
Life outside Star Trek
Roddenberry and her sister Dawn are from her father's first marriage to Eileen Anita Rexroat, after whom she was partially named.  She had a half-brother, Eugene "Rod" Roddenberry, Jr. from her father's second marriage to Majel Barrett. 
In the 1980s, she was a Reno, Nevada real estate agent, during which she became acquainted with Richard C. Datin, Jr., the very first Star Trek studio model-maker. With Datin, she was involved in that era with some social benefit events. (The Enterprise NCC 1701 and The Model Maker, p. 104)