Quote Originally Posted by Alleo View Post

Hm maybe I remember it wrong, but wasnt it said that the summoners gave Hydealyn the ability to split the essence of every thing? Why would you give her something like that if you dont intent to use it?
The same reason people don't use all their skills in a job or dungeon :P

But in all seriousness. It's because she's light aspected. Her ability to split something is at her disposal. The splitting of realities was a byproduct of what she split. Not exactly that she could split/bind etc.