What if, instead of creating her own friendship magic to solve the problem of Starswirl the Bearded’s unfinished spell, Twilight took the easy way out and just kept casting it until the ponies’ cutie marks were on the right way round again? Well I guess Princess Celestia would be all like “TWILIGHT I AM DISAPPOINT”. ‘Cause that’s kinda the magic equivalent of “solving” a Rubik’s Cube by taking it apart with a prybar and reassembling it.
(It’s also possible that the spell mixes the Elements of Harmony randomly, and there’s actually a 119-to-1 chance against the spell actually putting them all the right way round at any time, but I ignored that because that would make the cartoon waaaaaaay too long!)