I still haven't come quite to terms with it myself, but in your case I would suggest you think of yourself as two entirely separately people aside from the physical and vocal similarities. You exist, she exists, and no paradox was created by the both of you existing. Perhaps the "fictional" aspects of our realities comes from something along the lines of writers who genuinely believe they are creating something new, but really they're seeing over into our worlds.
This is what I've been trying to tell myself, at least.