Jehnna was the niece of Queen Taramis. As prophecized in the Scrolls of Skellos, her birthmark meant it was she who had to procure the Horn of Dagoth to bring about the god's rebirth, after which she was to be sacrificed to him. Her aunt kept this latter portion of the prophecy from Jehnna who willingly retrieved the horn and placed it in the forehead of Dagoth's statue.
As Taramis' grand vizier moved to cut Jehnna's throat, he was stopped by Zula. After Conan slew the transformed and monstrous Dagoth in a battle that followed, during which Taramis was killed, Jehnna succeeded her aunt as the queen of Shadizar. She chose Zula to replace Bombaata as captain of the elite guard, Malak to be her court jester and Akiro to be her personal wizard.
She wanted Conan himself to be her husband and king and rule Shadizar with her. But Conan's one and only love, Valeria, was dead, so he politely declined and went his own way.