In the 2360s, Lieutenant Leijten served on the USS Victory. It was during this time that she became good friends with Geordi La Forge while he served there, calling him her "little brother", and would occasionally give him advice with women. They later remarked that they made a good team. Leijten also had a relationship with Paul Bogrow. Initially, she thought he was "full of himself" and annoyed her, but, after a time, she thought she might have been wrong and had almost married him.
In 2362, the Victory received word that the staff of a Starfleet outpost on the planet Tarchannen III had disappeared. Leijten commanded an away team to investigate. She brought Lieutenant Geordi La Forge and Ensigns Anthony Brevelle, Paul Hickman, and Mendez. They found no signs of struggle, just the absence of the outpost staff and some tattered clothing. Without any more evidence, they abandoned the outpost; however, unbeknownst to them, they were all exposed to an alien retro-DNA that started to turn them into alien lifeforms.
In 2367, Leijten got word that three of her former crewmates had disappeared after she heard from a Federation supply ship that Hickman's stolen shuttlecraft was heading for Tarchannen III. When the pattern was recognized from her away mission five years prior, the USS Enterprise-D was contacted to investigate. She boarded and informed the senior staff, including La Forge, of the away team's mission and reviewed the sensor log. When they landed on the planet to investigate, Lieutenant Commander Leijten started to act strangely, refusing to leave. La Forge beamed her to sickbay where Dr. Crusher found that she was undergoing chemical changes. Later, she was covered with dark blotches and her hands began mutating. Alien DNA had started to change Leijten into an alien lifeform. However, Dr. Crusher performed a genetic treatment to reverse the effects. Commander Leijten then helped in the rescue of La Forge, who by that time was further along in his transformation and had returned to Tarchannen III. She talked him into coming back with her. (TNG: "Identity Crisis")
The historical video version of Leijten was described in the script notes as "Late twenties, striking, dynamic," following the conclusion of the video, the present Leijten was comparatively described as being "slightly older".
Her surname is spelled "Leijten" throughout the script, with the exception of two instances where the "jt" were transposed to read "Leitjen". The latter spelling was, however, the spelling used in the Star Trek: The Next Generation Companion (2nd ed., pp. 158 & 159) and the video game Star Trek: Starship Creator. According to her Starship Creator bio, Leijten was born in Sarasota, Florida to parents Doris and Paul Leitjen.