My immediate thought is to give her an experience more than a gift, though getting her unicorn and "occult" statues might be a thought as well? There should be services like that, especially with that "3D Printing" stuff that's been going on, anymore.

But really: take her out riding on the D-Wheel with you, go to a theme park-- even a water park, I know there's one near Domino City itself. And then go shopping at a nice clothing store, if she likes fashion, and see about getting an outfit for her. Maybe invite this Artemis girl she's friends with, too?

There's at least a limit of course, to not spoil her, but these are things I feel like even more normal families would do for a birthday.