Enter Mr. Sarcastic Rahandir Drakeskull. Shar said he is familliar with Gardon's magic and can break it under certain conditions so he may be possibly the one that releases her.
He only shows knowledge in the Undead Book, so we don't know if he is aware that Gardon uses such magic in the plot of the Human Book.
And why would he do that? What could he gain from doing this? With demons attacking and a civil war occuring, why would he divide the imperials even further at this point?