She is clearly not.
Her reasons For becoming Nightmare Moon were rather childish, "People sleep in my night shift so I will kill them all". Not to mention the fact that Unlike Scar who was treated as a second to Mufasa she and Celestia were treated as equals so her jealousy is pointless and childish.
Even SEPHIROTH is more sympathetic. "Mah Mommy is a test tupe" is better than "People sleep when I work"