A: Her Fairy Godmother of course!
Well, although the appearance of the Fairy Godmother to supply the gown is undoubtedly the most common version of the tale - there are others too.
The most popular and most-remembered version was written by Charles Perrault in 1697. His story introduced the Fairy Godmother who provided Cinderella with a beautiful ballgown and transformed a pumpkin into a coach to take her to the palace.
Tree Spirits ("Elder Mother") and Birds
In Grimm's Fairy Tales, such as Ashputtel/Aschenputtel, Cinderella is never visited by her Fairy Godmother at all. She must complete seemingly impossible tasks set to her by her Step-mother before she can attend the King's Feast. The tasks are completed by the birds, ants and other little animals to whom she has been kind. When even this fails to gain her leave to attend, Ashputtel prays and weeps at her Mother's grave, letting her tears water the hazel tree she herself planted. The ball runs three nights in succession and each night she finds a new dress, more beautiful than the previous, folded on top of the grave.
Alternatively, the dress is hanging or falls from the branches of the tree or is brought to her by the birds who earlier helped her to complete the other tasks. The birds also help alert the Prince to the step-sisters' deception when they cut off parts of their heels and toes to fit Ashputtel's shoe and later, at the wedding, they peck out those same offenders' eyes. But there is enough material there for another post ... and we were talking about the origin of the dress.
These versions nod towards tree spirits such as the dryads and tree worship in general. The tree is seemingly absent in other versions but the concept of the "Elder Mother" continues on in the Fairy Godmother.
Walt Disney, forever clever and sometimes misunderstood as one who "sanitized" fairy tales, actually did a fantastic job of working into his animated classic many of the symbols of the original tale. The befriending of the little birds and mice that perform a task and make-over the dress that had originally belonged to Cinderella's own mother. When her step-sisters destroy the dress, Cinderella runs in tears into the garden, where her Fairy Godmother appears and "Bibbity-Bobbity-Boo!"; she conjures up a majestic white gown. Clever, no?
Meadow Sweet Grove © V. Buchanan 2017