The role was very close to Ginger Rogers' heart. When she was touring America with her vaudeville act and chauffeured by her mother, Lela E. Rogers, they could not afford to pay the full fare. Ginger had to pretend to be younger by rolling her stockings down and holding her old dolly to look like a young child in order to get a cheaper fare.
It was decided to include scenes of Susan's (Ginger Rogers) mother. Spring Byington was the first choice but was appearing in another film. Rogers suggested her real mother Lela E. Rogers, who got the role.
When 'Sue-Sue' is asked by the two train conductors to prove she's of Swedish stock by saying something Swedish, she replies; 'I vant to be alone,' quoting the famous line spoken by Greta Garbo (who was originally from Sweden) in Menschen im Hotel (1932), which she parodied in her appearance in Ninotschka (1939), of which Billy Wilder was one of the screenwriters.
Billy Wilder was driving home from the studio one evening and pulled up at a red light next to Ray Milland. Impulsively, he called out, "I'm doing a picture. Would you like to be in it?", and the actor responded, "Sure." Wilder sent him the script, which Milland liked.