Well, demonic will either look like some nameless horror from the darkest depths of the abyss, or some goth with a little pair of bat wings stapled to her back, neither of which I find at all appealing. Angelic.
What about the best of both worlds? Most of the time you are angelic or at the most not really ugly like Peter Puppy here. But when you are mad/scared/annoyed/in pain etc you transform into a demonic really ugly monster. Like Peter Puppy here after he's transformed into a monster.