1) Hospitalised since 5 years old, with no friends, or life experiences, hence lack of perspective and sense of self.
2) Obsessed with book as a result of being hospitalised all her life.
3) Author's comments

If any one of these was lacking, it would be a lot less believable that she'd try to content herself with a meaningful death for the sake of the story, but as it turns out she has all of them.

But of course, the story starts a lot more light-hearted, and there's no real mention of her waiting for death. That's why as you start to see glimpses of her actually looking heading for it, you start to think, 'oh shit. isn't this story getting kind of dark'?

And after she various other things, the reveal that she actually WAS human, and hated her brother for being the protagonist, and hated her fate for being born as Origa despite her love for the books, it feels all the more shocking, lol.