When Ballard entered Starfleet Academy, she became close friends with Harry Kim, who lived across the hall in their student dorm. She taught him to ice skate, despite his dislike for cold weather. During her academy years, she never knew that Harry had a crush on her, and that being in the same classes as him was not a coincidence. Her favorite things to eat were peanut butter and jelly sandwiches; she seemed to live on them during her academy years. Her sloppiness sometimes caused Harry to ask for a baryon sweep of his room.
In 2371, Ballard graduated from Starfleet Academy as an ensign, and was posted to the newly commissioned USS Voyager, under the command of Captain Kathryn Janeway. There, she was reunited with Harry Kim. Her main post was in main engineering.
In 2373, Harry and Lyndsay were assigned to an away mission on a Class-M planet in the Vyntadi Expanse to investigate readings of dilithium ore. However, it was a trap by a Hirogen hunting party, who had reconfigured a power cell to give a false dilithium signal. During their retreat to the shuttle, Lyndsay was hit by an neural disruptor and died on the way back to Voyager. Harry gave the eulogy and she was buried in space.
Unknown to the Voyager crew, Ballard's body was recovered by the Kobali, who re-animated her as one of their own, named Jhet'leya. In 2376, she returned to Voyager and attempted to resume her life as Ballard. However, she discovered after a short time that her mind and body were no longer human. During her time away, she made a list of the things she wanted to do if she ever returned to Voyager. Eating Jibelian berry salad was #6, dazzling B'Elanna Torres was #16, hearing Harry play his music was #26, showing up for duty shifts was #27, and make Tuvok laugh was #32.
Ballard's favorite saying comes from an old Klingon battle cry: "Own the Day". She believed in attacking each day and possessing it. According to Harry, that's what made her so much fun to be around with. (VOY: "Ashes to Ashes")
She eventually returned to the Kobali when Voyager was being attacked by them. She came to realize that she didn't belong on Voyager anymore.