Her interest in movies grew while living near the motion picture studios, but she first took a job working as a doctor's secretary and assistant, then using her spare time to look for film-related jobs on the side. While modelling in Los Angeles and making uncredited appearances in films, she was chosen for a small role in the wartime B-movie melodrama
Parachute Nurse (1942). The Hollywood producer
Sol Lesser and later president of the Sol Lesser Productions Inc., often looking for new faces and unknown talent, signed Riordan as a contract player after she approached him about possible roles. Many well known film screen, stage and radio stars were featured in the films various stage performances, but Lesser purposely went against conventions and cast other unknowns for the main story acting roles. The other newly contracted players featured in addition to Riordan included Lon McCallister,
Margaret Early,
Sunset Carson (as Michael Harrison) and
Cheryl Walker, a former “stand-in” for actresses
Veronica Lake,
Claudette Colbert and
Madeleine Carroll. Shortly afterwards, Riordan's contract was transferred to
Warner Bros. where she was cast as
Bette Davis's daughter Fanny Jr. in
Mr. Skeffington (1944). In 1945, she went on to act alongside
Basil Rathbone and
Nigel Bruce in a
Universal Pictures produced film titled
Pursuit to Algiers (1945) where she had both an acting and singing performance role. Riordan often took part in various activities related to the war effort campaigns that were common during 1941–1945 by participating in
USO canteen activities and other services that were provided to enlisted U.S. military members. She also assisted in the fundraising efforts that were part of the joint Navy and Red Cross campaign to sell
war bonds to help raise money that would go towards building the cruiser
USS Los Angeles. The wartime effort activities she participated in along with the increased visibility that the film
Stage Door Canteen had brought, and her modelling experience, among
G.Is. On June 25, 1945, as part of the widespread “help the war effort campaigns”, the California department of motor vehicles bestowed the title of “Share - the - Ride - Girl” upon Riordan to help the war effort by encouraging motorist to share their cars. She continued to appear in film supporting roles into the 1950s, while attending graduate school to study speech pathology, which later evolved into the study of clinical psychology. After she further developed a career as a clinical psychologist, she eventually gave up acting altogether. == Personal life ==