I've not heard that theory, but all I can say is that I'm really looking forward to see how the story unfolds. Her introduction as a companion has been genius.
My theory is that she has been split throughout the Doctor's timeline in order to save him at crucial points in his life. If the season finale is set on Trenzalore - this is probably where the Doctor's final resting place is and full of time energy. That's where she'll get splintered through time.
A cosmos without The Doctor scarcely bears thinking about...