Heh heh, our sweet little Miss Tetra is not a Gerudo.
First of all, she’s outside all day, commanding and many other things. It’s outside, and the sun is outside. She’s a full Hylian, getting a lovely and natural tan outside.
Here’s one more reason why I’m quite sure she’s not a Gerudo:
Spoiler (Highlight to read):
In Hyrule Castle, when the pieces of the Triforce of Wisdom are put back together, Miss Tetra transforms in Princess Zelda. Note that her skin is a pale color. That’s proof that’s she 100% Hylian. 
Yeah, I think you understand.