The answer is:Just watched the finale too, and my big question is from the Library.
I actually guessed who she was part way through, but at the crib scene when he figured out, I suddenly thought she was his mother. That's what I get for thinking twice about my guesses.Why did she not regenerate?
too much energy, same reason she took the Doctor's place to save his life (he wouldn't have been able to regenerate either). And the reason she couldn't be teleported out of the computer like the other "saved" library patrons were was because her body was dead, only her consciousness in the screwdriver got uploaded, much like the ones who were eaten by the shadows.
another trip to the Library might be in order at some point.