The Prince was under a charm spell that the Dumb Savior was unconsciously giving out. She's a selfish and childish dumbass who doesn't understand nor care about her responsibilities but nothing more than that.
<Tsukina> * Doesn't need to ask to be pretty and charming because she already is pretty and charming *
I'm guessing this barrier will be so OP they'll realize she's another "Savior". Good to see if - even for a moment - the prince was released from the charm spell.