Betty was high school principal William Hastings' secretary.
Around 2014, Dale Cooper's doppelganger was in pursuit of a set of coordinates which Betty possessed, and he hired Ray Monroe to obtain them. These were the coordinates which "the Major" had asked Hastings to obtain while he was in "the Zone" with Ruth Davenport.
By late September, despite his detainment in federal prison, Ray had apparently succeeded in obtaining the coordinates, and attempted to extort Cooper for $500,000 in exchange for the information. Betty was killed in her car by a bomb planted by Cooper and Jack.