Mews’s professional career began as a teenager in New York City. Dustin Hoffman, not yet famous, gave Mews her first role, acting and singing in a play he was directing. She went on to act in many leading roles in resident theatres all over the East Coast.
In 1966, Maria von Trapp came to Mews’s (then Mary Small Rusk) opening night as the lead in The Sound of Music. At the end of the show, there was a standing ovation and Mrs. Trapp stood up, hugged Mews, and said, “I have seen many Marias, but tonight it was I. There couldn't be a better Maria.” She then invited Mews to perform with her at the Montreal World’s Fair, where Mews stunned the crowed of 20, 000.