Within a Sanctuary just built for her, a earth pony with secret knowledge is kept there outside from the world. So to obtain what she knows, the Princesses kept her there to only paint every few seasons, of her dreams and visions of another world.
Fluttershy had disappeared from a strange mist that covered most of Equestria for weeks. She, after being out in the mist for so long seemed to wandered off to the Everfree forest and in a strange side effect had lost her memory. Only to find a leaf.