ok, keep the she-demon part in, but have her try to destroy Equestria and The Mirror World instead. to save the day, The Rainbooms use the Mirror World versions of The Elements of Harmony. i still stand by my point that Sunset should go to detention afterwards, though. i think that'll make more sense for her redemption arc.
so, the Mirror World isn't a direct "reflection" (pardon the pun) of Equestria, and the characters' ages aren't the same? that's where my confusion lies. i'd always assumed the pony CMC were seven or eight, while The Mane Six were 14-17 (making them adults in pony years)