Even if you somehow evoke an epiphany in the Ancient Dragon, she still has millennia of bad habits and assumptions. I can just see the confused dragon wondering what all the fuss is about as she finishes up snacking on that flock of sheep, and that shepherd or two.
And, yes, turning her loose in all her evil glory out onto the enemy's already oppressed peoples is not going to look good on your quarterly evaluations.
That's as may be, but from personal experience once those epiphanies start, if they're real, it's hard to stop them from continuing.
Besides, that sounds like *wonderful* role play territory; depending on the conscience of the player characters, they may feel somewhat responsible for the dragon's actions at this point and there may be a need to shepherd her growth.