It wasn't Talana that was being controlled. You were. Ygerna says so. You were mentally in a very weak state because of the lapse in the Dragon Slayer ritual, which was Rhode's fault. Talana may have been controlled to some degree - coercing a dying Dragon Knight, the last of her kind, into giving another her power wouldn't have been too difficult - but not necessarily. Zandalor was wrong about the influence of the Soul Forge spell. I didn't see any big loopholes there. Ygerna's a powerful sorceress, yes, but more cunning than powerful. She abused your weak mental state to influence your thoughts - as you can easily tell from playing the game.
Therefore, also, turned out the Dragon Slayers were right all along. Dragon Knights should be exterminated, because they are extremely powerful, but still only possess the mind of a human, which is too easy to control. No man should have that kind of power, even to do good, as doing good may inadvertantly cause irreparable harm.
