Cassie is the alter ego of Kasidy Yates in Benjamin Sisko's visions from the Prophets and Elias Vaughn's second orb experience.
Cassie was Benny Russell's girlfriend and was pregnant with their child. (DS9 novel: Unity)
After Benny had been removed from the asylum and sent to jail in 1955, Cassie enlisted the aid of Kay Eaton to get him out. (ST - Typhon Pact novel: Plagues of Night)