I must say, there is some justice to the position held by the Dryad who was in the Tower.
Why could they not have periodically traded places?
This argument that they are the same person, it doesn't hold water after enough time has passed with no similar experiences; clearly they will start to diverge, to be separate existences.
After all, they aren't able to share what they experience between them, so it cannot be said they are having equal existences.
Such being the case, the one tasked to stay inside the Tower, having no unpleasant experiences, naturally becomes hostile to those who set her this duty.
A thousand years of vigilance, with no rest, no respite, no one expressing appreciation for what you are doing? And no longer able to leave voluntarily?
How does this differ from those imprisoned, those you are to suppress?