"Yes, but not in the way you're thinking. She draws her energy from the time vortex, from the universe itself. She can remain in the vortex itself indefinitely." The Doctor tucked his hands into his pockets and started rocking back and forth on the balls of his feet, having been still for longer than was entirely comfortable for him.
"I'm sorry, John. I really am, but there's nothing I can do about our situation just now. I'm just trying to help you see that so you understand why I can't take you back to 1913."