@dethduck as powerful as she is, the hero is way stronger, plus is completely mindless, so the country can use him as a wmd, and then add him to their bloodline, which is where the princess gets all her power, all the past heroes in her family tree.
@dethduck
It's a matter of duty. As the Princess, bringing the Hero to her kingdom is her divine purpose.
If she cannot do that, the people of her world can no longer trust her family.
If her family cannot be trusted, the people of her world will no longer be united and opportunists will exploit that weakness.