Fenna was the alter ego of Nidell who was created when Nidell lost control of her psychoprojective telepathy. Fenna was actually a being of pure energy, a doppelganger for Nidell.

While Nidell and her husband, Gideon Seyetik, visited Deep Space 9 on the USS Prometheus in 2370, Fenna appeared on the Promenade. Fenna, outgoing and passionate, was the direct opposite of Nidell. Benjamin Sisko fell in love with her. He was surprised when he met Nidell on the Prometheus and found out what was happening. Her manifestation was killing Nidell due to the extreme stress of projecting Fenna. When Fenna realized she was a projection of Nidell, she returned to Nidell to save her life. (DS9: "Second Sight")