To my most faithful student, Twilight Sparkle,
The Mirror Pool's mechanism is one of those things that I would be a great deal happier without, yes.
A cloning spell... Well, admittedly nopony I know of has tried such a magical working, or at least nopony that was serious about it. Either way I'm very proud of you for going through the proper steps, and being very, very careful.
Also remember that as this spell has the potential to create sapient life, you'll need to appear in-pony for an evaluation before you can be licensed to cast it. I hope you have a good reason for making this spell Twilight, because it is immoral and dangerous to create a new mind that will call (or worse, split) a soul for a reason that isn't dire.
Your loving mentor,
Princess CelestiaPS. I'm sorry it took so much pain for you to learn to go through the correct steps before something can go wrong.