Buck Privates was an early-1941 Abbott and Costello film, which introduced the Don Raye/Hughie Prince jump blues called “Boogie Woogie Bugle Boy,” sung by the Andrews Sisters. As technology improved, it was no longer required to have three singers to do three vocal parts, as Bette Midler will readily testify.
And there things stood, until further technology permitted a single singer to triplicate herself on camera:
Michelle Creber is seventeen; among other things, she’s the voice of Apple Bloom on My Little Pony: Friendship is Magic. Here she looks kind of Carol Burnett-y, which fits: like Burnett, she has a gift for physical comedy, and also like Burnett, she has killer gams.