Who or what was the Childlike Empress?

I’ve only read The Never Ending Story and, from what I can recall all creatures of Fantastica are equal, in the sense of having been created by the imagination of a human in one of the “cycles” on the never-ending story.

We’re however lead to believe the Childlike Empress is a singular entity, distinct in nature to all the rest of the creatures and intrinsically connected to Fantastica itself.

Are there any licenced works that explore or extend the Childlike Empress’ backstory?