Royal by blood or marriage: By blood, although her evil stepmother has taken Snow White's rightful place as heiress to the kingdom.
Proof she's a princess: So much, but let's start with the ferocious troll that she tames by just looking at it. Not many can put human-eating monsters under a spell with just a glance. Also, she's able to communicate with birds, and though being kept in solitary confinement for a large percentage of her young life, her skin and hair are somehow not grotesque.
Adorable sidekicks: The aforementioned birds. And a trusty white horse comes to her rescue on occasion. Also, pixie creatures emerge to greet her, although their adorableness is debatable.