I have never seen anyone with red eyes in my entire life, either in person or online.
Even people with albinism have gray or light blue eyes, not red.
Red eyes due to albinism is more commonly seen in animals like rodents, but it's not completely unheard of in humans, which can also appear pink or even violet. That said, I doubt Luna is an albino, as her hair is black. True albinos typically have white or off-white hair.
I think the better explanation is simply that she's ... unusual. Given that she possesses supernatural powers in a setting that is essentially high fantasy, this really shouldn't come as a surprise.