By who, the keyblade community, your family ,the world
How about logic?
Sora is not a Prince. He's a 'hero', but not a Prince. And we all know that much that yes, a strong heart means they fare better against the darkness. However...
It doesn't mean they have 'heroic' qualities. Otherwise, Maleficent would be considered a heroine because of her strong heart.
So yeah. I'll use logic and deduce that Kairi hasn't done any of those three things. She's not a hero. She's not of royalty (from what we've seen) and she's not a woman... I mean Leech... I mean, married to a Prince.