It's called a Doppel. You know how Grief Seeds draw impurities from our Soul Gems, but you probably don't know the why. Those impurities are partially made of despair, anger, and other negative emotions, the same things that make up a Witch's body. They drain it out of Soul Gems to try to regain their form.

I can expel those impurities without a Grief Seed, and my Doppel is a side effect of that. The reason she looks so much like a Witch is because they're made of the same stuff, but Ophelia listens to me because everything that goes into her is still my emotions. Make sense?