The character's name is Olivia, who is hired by the MIB in 1969 as a secretary. Her smarts eventually find her running the whole operation a few years down the line. In the film, Will Smith's Agent J is forced to travel back in time so that he can team up with former partner Agent K (the 1969 version will be played by Josh Brolin, while the present day version will be played by Tommy Lee Jones) to save the world.
Men in Black III is currently on haitus while third act story problems and a new ending are hammered out. Maybe we'll eventually learn what happened to Johnny Knoxville's character from Men In Black II, a sequel that really should have taken a hiatus to figure out its ending.
Men in Black 3 was released May 25th, 2012 and stars Will Smith, Tommy Lee Jones, Josh Brolin, Jemaine Clement, Emma Thompson, Michael Stuhlbarg, Mike Colter, Nicole Scherzinger. The film is directed by Barry Sonnenfeld.