We love a good inspiration story: Gail Carson Levine came up with the idea of having Ella be under a curse because she was annoyed by Cinderella's obedience and kindness to her awful stepfamily. The curse helped explain it in a way that made sense to Levine and made the character more sympathetic. (source)
Levine started her story in a writing course and based it on "Cinderella" since she couldn't think of a plot and the fairy tale already had a plot ready to go. Hey, plots are hard. There's a reason Hollywood keeps remaking Spiderman.
The earliest recorded version of "Cinderella" comes from 9th century China. Rather than a fairy godmother helping the heroine, a magical fish is her benefactor. The tale still has the ID-by-shoe motif, though, which makes sense given that small feet were thought to be especially beautiful in China, leading to the practice of foot-binding.