Kate "The Brigadier's daughter" Stewart is currently in charge of UNIT and was played by Beverley Cressman. This error was fixed and Jemma Redgrave would later take on the role. Kate is known for saying "science leads" and paying no attention to her completely incompetent military.
She is also an astounding bridge player.
Kate Stewart is the daughter of Brigadier Lethbridge Stewart, a fact which the show likes to treat as her only characteristic. When she isn't parroting famous quotes of his, she's making awful tactical decisions, driving to a foreign and potentially dangerous location with no backup and ignoring perfect opportunities to kill the Mattress.