Link taps at the Slate, before turning it around to show the same picture of Mija that Link showed Luke.

The picture makes it pretty clear just why she's a 'Great' Fairy: from the size of the trees and the way the camera is angled up, it's clear that she does't just tower over link: she's the size of a building.

"They enchant clothes when you give them things," Link explains. Hence the idea that Vader's clothes might have been enchanted by one.