Surely, it should be about getting the right actor for the role? I mean, if you're doing historical, it's important to get things like race right - which folk never do (like 300, Gerard Butler is no more Greek than I am!). But fairy tales?
I mean, if Ariels father is King Triton, then she should be Greek as well, right? Well no, because Anderson was Danish! Ah. then they should have cast Sandi Toksvig? Thought not!
Listen, this kid can act, she can sing, she's the right age, she's easy on the eye and she wants to do the part. That's all you need, because this is a fairy tale, not kitchen-sink social realism!
Also, not to put too fine a point on it, this is bloody Disney! Since when did Disney care about tradition, logic, realism or indeed anything except the bottom line? And you know as well as I do that there's nothing like a bit of controversy to put bums on seats! The only thing Disney cares about in terms of colour is keeping their accounts in the black!