Ani is our main gal, so it makes sense that we see the story through her eyes, but this doesn't mean she has to give us the lowdown herself. She's a princess, after all, so it's only fitting that there's someone else to do this for her. And for us as readers, having an outside narrator who can clue us into the bigger picture from time to time gives us a fuller story than we might otherwise get from our teenaged main character.
Don't believe us? Check this sentence out:
She stopped in the shadowy corner of the wall and greeted Falada. His mane was still damp, though his hide fared well in the wild weather. His glass eyes looked indifferently at the stones of the city. (16.1)
Notice how we hear what Ani's going through—stopping and saying hello to her horse—but it's not her speaking to us? Instead our narrator is like a fly on a wall, and because of this we get a bit more information about Falada and the scene than we might if we were stuck in Ani's head. And luckily for us, our narrator is totally capable of buzzing into Ani's brain from time to time, so we also get to know her thoughts pretty well, which helps us care about the journey she's on.
Ani's perspective is the only one we get, however, which is fitting since she has such a hard time relating to and understanding other people. They're a bit of a mystery to her, and since the narrator can't access their thoughts, they're a bit of a mystery to us too. Cool, right? Plus a prince can't be brooding and mysterious if the narrator can read his mind, and that's just no fun.