[little cinder girl]. Heroine of a fairy tale. She is the drudge of the house, dirty with housework, while her elder sisters go to fine balls. At length a fairy enables her to go to the prince's ball; the prince falls in love with her, and she is discovered by means of a glass slipper which she drops, and which will fit no foot but her own.
The glass slipper is a mistranslation of pantoufle en vair (a fur slipper), not en verre. (R. C. Perrault: Contes de Fées.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894