Sheik's design in Brawl was based off of unused Twilight Princess Concept
One source states, "Sheik is one of the most beloved characters in the Zelda universe and for good reason. The revelation of her identity was a fantastic twist back in the days of Ocarina Of Time and though it's not shown, Shiek would have to be a serious badass to survive in a world overrun by Ganondorf. Smash Bros. Melee confirms this suspicion and reveals Sheik as the all-out ninja she truly is.
Sheik returned once more in Brawl, though her design got an upgrade. She now has a tightly bound ponytail, a dagger, bandages on her legs, and a more crisp looking outfit. This design is based off of concept art for Twilight Princess, but sadly Sheik's inclusion in the game was scrapped well before its release. This is a shame, for seeing Sheik in the world of Twilight Princess would have been a real treat"(Reid).
