Kitty Kowalski doesn't belong to the mainstream of the DC-Universe. She was created for the movie Superman Returns and was played by the actress Parker Posey. She was created by Bryan Singer, Michael Dougherty and Dan Harris.
The character of Kitty is based on the charachter Eve Teschmacher from the movie Superman (1978). Like Teschmacher, Kitty is a henchwoman of Lex Luthor.
Before the movie
Kitty worked as a prison nurse in the prison where Lex Luthor was locked up. At their first meeting, Kitty watched him killing another prisoner. He tried to kill her to but Kitty told him that she is his biggest fan and she can help him. Since this day, Kitty and Lex worked together. She knows about his plans and after he was released, Lex hired her as his henchwoman.
Lex traveled with Kitty and his henchmen to the Fortress of Solitude and steals some of the kryptonian crystals. He needs these crystals for an experiment that causes a power outage in the eastcoast of america. After his plan, to create a new landmass, was stopped, Kitty and Lew escaped in one of their helicopters. Both are stranded on a lonley island when their helicopter runs out of fuel.