Born in Harrisburg, Illinois, she was the daughter of musician Dewey Alphaleta (née Todd) and businessman Edward William Gregg. She had a stepsister, Mary. Gregg was a prolific radio actress, heard on such programs as The Adventures of Sam Spade, Dragnet, Dr. Kildare, Gunsmoke, The Jack Benny Program, Let George Do It, Lux Radio Theatre, One Man's Family, Yours Truly, Johnny Dollar, The Screen Guild Theater, CBS Radio Mystery Theatre, The Zero Hour, and Mutual Radio Theater. On the radio series Have Gun–Will Travel (starring John Dehner as Paladin), Gregg portrayed Miss Wong (Hey Boy's girlfriend), and also appeared in very different roles in the concurrent television series with Richard Boone. She had the role of Betty Barbour on One Man's Family and played Richard Diamond's girlfriend, the wealthy Helen Asher, on the radio series Richard Diamond, Private Detective (starring Dick Powell as Diamond). She later guest-starred in an episode of the television version of Richard Diamond, starring David Janssen.