There was a glass slipper in the PV. Do you think they'll explain why the franchise is called Cinderella Girls? Or have they already explained that?
Okay I see people didn't watch the pilot. There was a glass shoe in that one too, only falling into water rather than rolling out of a box. But also, IIRC, the pumpkin. More importantly, all the transformation sequences and other Cinderella things.
Note, however, that they got some of the mythology backwards from the fairy tale. In the pilot, girls transform into idols at the strike of the midnight, whereas in the fairy tale, Cinderella's transformation unrolled in the opposite direction. Not exactly sure what's up with that.