Find Sheik?

It didn't take long for Link to decide that Sheik was definitely the person to ask about this. He seemed to be an expert on all sorts of magic, so something like this transformation might be something he knows about. Of course, that left the problem of finding the Sheikah boy. He didn't seem to have a home, or anywhere else Link could reliably find him. In fact, he mostly seemed to just appear while Link was on the trail to the next dungeon, so he could teach Link a song. That meant ignoring these changes and continuing on towards the next temple.

Knowing that the next temple was the Water Temple, Link headed towards the Zora's Domain. Epona was a little wary of his new body at first, but after sniffing his hand a little she warmed up to him again. Still, this body was a lot softer than usual, and didn't have the experience riding a horse that it usually did. It took a lot of trial and error to get all the way to the Domain, but once there he dismounted from his horse, played Zelda's Lullaby on his ocarina, and headed inside.

The home of the Zora's was cursed, as he felt as soon as he entered. The temperature dropped suddenly and drastically, and Link found the cave system covered in thick sheets of ice, the Zora themselves frozen in it. Even the king of the Zoras was frozen solid. Hoping Jabu Jabu could help, Link went outside and found that he was gone as well, and the Zora's Fountain had large slabs of ice floating on the surface. However, Link's sharp eyes spotted a cave that was now reachable, if he used the ice to his advantage. Once inside the cave, he fought through puzzles and monsters to reach the end. The puzzles actually seemed easier than normal, his mind moving through them quicker than usual. Fighting monsters, on the other hand, seemed much more difficult. He wasn't used to wielding the Master Sword as a woman, and he didn't have the fighting physique he was used to. It was only with quick thinking and luck that he managed to survive to the end. Once there, he found a chest that contained a set of Iron Boots, and turned to find Sheik there.

For once, Sheik looked as surprised as he did. "Link? Is that you?" he asked. Link nodded, and Sheik shook his head. "This is an unexpected problem. You've been gifted with the power of a Great Fairy. With time, you'll probably have as much magical power as the Sages, or more. But you clearly need to completely restart your sword training."

Link asked if there was any possible way to reverse the curse.

It seemed as though Sheik smiled in response through his cowl. "This isn't a curse, it's a wish. And I don't know if it's possible to reverse it. I'll look into that, but for the time being you need to go to Lake Hylia, where the Water Temple is. Princess Ruto is the only Zora left unfrozen, and she has already headed there to try and break the spell cast upon her people. Go, Hero, and save her."