In 2377, she became involved with Starfleet Lieutenant Reginald Barclay while working on a Ferengi casino ship, though she told him she was a teacher. Barclay discussed details of his work at the Pathfinder Project with Leosa, which she then sold to the Ferengi Nunk, who used the information to intercept a holographic transmission Barclay sent to the USS Voyager. After she had gained all she needed, Leosa left Barclay without notice.
When Barclay realized she was behind the failed transmission, Leosa was brought in for questioning, though she initially denied any wrong doing. It was only after Counselor Deanna Troi threatened to send her for "extended" psychiatric observation that she admitted to her participation in the crime, revealing it was Nunk's plan to obtain some of Seven of Nine's nanoprobes which he would then sell for huge profit. She later identified the ship Nunk was using to carry out his plan and said she was going to get ten percent of any sale as payment. (VOY: "Inside Man")