Who was the first Cinderella?

In her hugely enjoyable book, From the Beast to the Blonde: On Fairy Tales and Their Tellers (first published in 1994 -- mine is the Vintage's 1995 version) the mythographer, novelist and historian Marina Warner answers:

The earliest extant version of ‘Cinderella’ to feature a lost slipper was written down around AD 850-60 in China[.]

She continues:

The Chinese Cinderella, Yeh-hsien, is ‘intelligent, and good at making pottery on the wheel’. When her own mother dies, and is soon followed by her father, her father’s co-wife begins to maltreat her, and to prefer her own daughter. A magic golden fish appears in a pond and befriends Yeh-hsien. When the wicked stepmother discovers this source of comfort for her hated stepdaughter, she kills it, eats it and hides the bones ‘under the dull hill’. When Yeh-hsien, all unknowing, calls to the fish the next day as is her custom, an enchanter descends from the sky and tells her where to find the bones: ‘Take [them] and hide them in your room. Whatever you want, you have only to pray to them for it…’ Yeh-hsien does so, and finds that she no longer suffers from hunger or thirst or cold — the fishbones care for her. On the day of the local festival, her stepmother and stepsister order her to stay behind, but she waits till they have left, and then, in a cloak of kingfisher feathers and gold shoes, she joins them at the festival. Her sister recognizes her, and it is when Yeh-hsien realizes this and runs away that she loses one of her gold shoes. It is picked up and sold to a local warlord: ‘it was an inch too small even for the one among them that had the smallest foot. He ordered all the women in his kingdom to try it on. But there was not one that it fitted. It was as light as down and made no noise even when treading on stone.

Yeh-hsien comes forward and, taking her fishbones with her, becomes ‘chief wife’ in the king’s household. Her stepmother and sister are stoned to death. (p. 202)