With season 2 already on the way, I'm all but convinced this is a plot point that will come back to haunt the Spellmans along with their regular demons and ghosts. There hasn't yet been any reference to one specific family secret in CAOS, but that's probably because this particular version of the Spellman family seems to have hundreds. If Hilda had been keeping Sabrina's Christian baptism secret and Zelda hiding that her father had promised Sabrina to the Dark Lord when she was a baby, would anyone be surprised if another secret was up their sleeves? And if there really is an evil twin, who's to say that twin wouldn't be — *huge gasp* — Sabrina herself?