I'm guessing the pointy ears, as well as those spikes on her shoulders, are either clip-ons she adds for flair or just the side effect of being in contact with Queen Metalia.
In Act 7 we can see her current-day human self exploring the North Pole before she frees Metalia, and while she's too far away to make out her ears and she's covered in winter gear so we can't see her shoulders, I always figured that backstory hints that she was reborn as a normal human and then became evil, pointy ears and spikes and all, after coming in contact with Metalia again.