In 2371, two Cardassian scientists, Gilora Rejal and Ulani Belor, were chosen by the Cardassian Union to assist in an effort to place a wormhole relay station in the Gamma Quadrant to aid communications and to provide an advance warning of a Dominion attack.
The Obsidian Order, angry at the recently signed Bajoran-Cardassian Treaty, sent Dejar to Deep Space 9 to sabotage the attempt, posing as a third scientist. She sabotaged the USS Defiant's main emitter coupling. When the ship fired at a comet that was about to destroy the Bajoran wormhole, it shattered the comet instead of vaporizing it as planned.
Gilora did not wish Miles O'Brien to be blamed for incompetence resulting in the malfunction and she revealed Dejar's status as an Obsidian Order operative. Dejar was taken to quarters and confined. Gilora was not worried over exposing her, telling O'Brien that the Order would not look kindly on Dejar's failure. (DS9: "Destiny")