Kitten was an eleven-year-old girl whose parents were killed in a train wreck. She became the ward of David Merrywether
(Cat-Man). Discovering his ward was a trained acrobat, David decided to train her as his crime-fighting sidekick. As the girl grew into a woman the relationship became more complex. She was already grown up by the time the original Cat-Man series ended.
AC has reconned her history somewhat. Their versions of Cat-Man and Kitten did meet in World War II but Katie was already twenty-years-old at the time. The two married after years of courtship. They were among the heroes to enter the Vault, preserved in suspended animation until needed again. They went into their long sleep in the 1950s and emerged in the 1980s, youthful as ever but feeling out of place. At least one familiar face was waiting to greet them, Dr. Macabre. Their archenemy from their past had also been in suspended animation and emerged to continue their conflict.
In the new Project Superpowers Kitten is back along with Cat-Man after being imprison by the Fighting Yank in the Urn of Pandora for sixty years. Unfortunately for Kitten, Cat-Man has changed after his imprisonment into a much more feral Superhero. Kitten joined a group of sidekicks called the Inheritors and found him but they have not been able to help Cat-Man.