Kay is the first child of Adam Destine and his genie lover, the first in a long line of brothers and sisters. With the extreme longevity of the Clan coupled with "Cuckoo's" penchant for body-hopping, Kay has held many identities and lived many of lifetimes. At one point, when adventuring with her sister, "Gracie", they, with Professor Xavier were responsible for releasing the demon Synraith into our reality, and although it was soon defeated. (This was many years before Xavier went on to form his team of mutant heroes known as the X-Men.)
It is unknown how often she would stay with the rest of the family, but she was apparently on hand when Adam killed his son, Vincent, and created a rift among the family. This and other factors led to the family to scatter around the globe, adopting the so-called "Relative Strangers Protocol". The family feared that should their existence become public, they would face undue persecution and hardship. Cuckoo adopted the identity of the head of an exclusive fashion design company.
Eventually, the existence of the family was discovered and the members began to be systematically murdered. Kay was one of the first killed, but she used her psychic abilities to find a recently accosted prostitute and took over her dead body. Cuckoo was instrumental in coordinating the other family members into defeated their enemies, and in staying together as a family once again.
Kay used her psychic abilities to convince her co-workers that her new body was the heir to Kay's fortune, and she assumed control of Kay Cera's fashion designs once again. This led to an assassination attempt on herself, but this was stopped by her family members, Rory and Pandora, with Spider-Man in tow.
When the demon Synraith tried to enter Earth's dimension, it drew Cuckoo and the others responsible for its containment (including Professor X) together again. A brief misunderstanding allowed the two families of X-Men and ClanDestine to scuffle, but soon the demon was defeated, killed as the heroes closed its dimensional gate.