Nidell was a Halanan female and the ninth and last wife of noted terraformer Gideon Seyetik. She was the daughter of a local dignitary. Her species had an unusual ability known as psychoprojective telepathy. Nidell lost control of hers, creating a doppelganger, Fenna.
After Gideon had finished terraforming New Halana, he was feted by the Halanans. During the unveiling of a statue dedicated to his honor, he met Nidell. She was, according to Gideon, infaturated with him from the start. He promised that he would show the galaxy to her, which was a very enticing prospect as she had never left her world.
In 2370, again when she was distraught, she created the doppleganger Fenna, who fell in love with Benjamin Sisko. When Sisko met Nidell in the quarters aboard the USS Prometheus she shared with her husband, he at first thought it was Fenna. Seyetik later explained his wife's telepathic ability.
In order to save Nidell, Seyetik killed committed suicide by flying a shuttle into a dead star and thus regenerating it. She recovered and did not remember her experiences as Fenna. She returned to New Halana, where she would live out the rest of her life. (DS9: "Second Sight")