I'm with Scalla - from the way it's explained in the end of the story, and this made sense to me, when you first meet Talana at the Bellagar Shrine in Broken Valley, and she's in human form, that's Talana. She grants you the dragon power, and you enter a dream sequence where you are in dragon form. At that point, Talana is already dead and is no longer talking to you, but there is a voice which sounds the same as Talana, and that's Ygerna being an opportunist, leading you to believe she's Talana.