My daughter's favourite film is Grease (1978), I have watched this film with her many times and always wondered why the cast chosen are clearly in their 20s and 30s. Stockard Channing played teen-aged Rizzo (the video clip below she is in the purple shirt) at the age of 34! The film contains a song called 'Look at me I'm Sandra Dee' which until I watched Imitation of Life (1959) I had no idea Miss Dee was a real person.
Sandra Dee had the same 'girl next door' wholesome image as Miss Day. She did not make many films but all were ingénue roles which is why she and Oliver Newton Johns' Sandy Olson character in Grease were mimicked in the following sequence.