The thing with heavenly gifts is that they don't always take mortal sentiment into account. This is true for everything in Sirius' person, past, present and future, but is especially evident in her eyes specifically.
They say beauty is in the eye of the beholder, but in this case, her eyes range only from kind of unsettling to outright horrifying.
Most people have any sort of eyelids right above their eyes, and eyebrows above those. Sirius doesn't. Not... quite. On top of her human eyes there's a second pair of them, separated by a fold of thin skin. This second pair is usually half-closed in order to keep the first pair completely open. When this first half closes (for example, when she sleeps, or blinks), this sort of eyelids cover them entirely, and the second pair opens and keeps watch.
Only the second pair has darkvision, but they are never fully closed so it's never been an issue. Well, it's been all sorts of issue, but losing darkvision was never one of them.
Losing her family? Yeah. Losing friends? Of course. Losing the chance of enjoying an ordinary life? Well, she's never been ordinary to begin with.
All four eyes move independently, at different speeds, and the top pair is slightly wider, granting her a bit more of peripheral vision. All four scleras are white, normal, but the irises are a little bigger than they should be, in a sort of pearlescent grey, and pupilless, hence the reason why she was assumed to be blind at birth.
In time, she found that covering them was the only way to go unnoticed, and even make the most out of them by hiding her clear advantage, but it still hurts, just a little, to be pointed at or to scare people who are genuinely good, and should, perhaps, see in her an envoy of angelic good and lawfulness, rather than an abomination.
