The mirror-universe Jennifer Sisko is a Terran scientist and the estranged wife of the rebel leader, who builds a sensor array for the Alliance until the prime-universe Sisko persuades her to defect.
In the mirror universe Jennifer Sisko is alive, and has long been separated from a husband she regards as a selfish pirate. Hoping to end the bloodshed quickly, she works for the Alliance on Terok Nor, developing a transpectral sensor array that would let its ships find the rebels hiding in the Badlands.
In Through the Looking Glass the rebels bring the prime-universe Benjamin Sisko across to impersonate her dead husband and win her over; failing that, they intend to kill her. Sisko, shaken at seeing his late wife's double, convinces her to leave with him. She realises he is not her husband, but joins the rebels anyway.
She returns in Shattered Mirror, where she lures Jake Sisko to her universe and is killed protecting him.