@Eric and anyone else who doesn't get it.
The above is Wildfire, the semi-famous OC of Sabrina Alberghetti (Sibsy) who is Studio B's lead story-board artist.
She is also heavily involved with the fans on DeviantArt and EQD.
It seems she was able to get her OC into that first Cadence flash-back:

Now I wonder if Lauren Faust's OC will make it into the show. I could see them showing her as Celestia and Luna's mom, since a lot of the fandom has latched on to that idea.