She was the only alien in the movie to be played by a live-action actress, namely Lisa Marie Smith.
She appears after the attack at the US Congress, when the Martian Leader discovers the president's location. She is taken to the White House by the Press Secretary Jerry Ross (a ladies man who thinks she is a prostitute, who also has a bad habit of taking women into the White House for his own pleasure). He takes the spy to a secret lounge, unaware he is being watched from the Leader's saucer. At the lounge, the spy kills Jerry by smacking him in the head with a bronze sculpture, then heads for the presidential bedroom where President James Dale and First Lady Marsha are sleeping. She removes her mask revealing her true Martian face and tries to shoot the President, but is distracted by Marsha, who calls for security as the spy holds Dale as a hostage. However, she is distracted by a bird, causing the president to escape her hold and the guards to shoot her in the head, killing her instantly.