Can you describe the "elemental form" a little more or is it up to interpretation? You said she looks kind of like a fairy, so wings of sorts or just a wispy sort of body?
She should have wings on her back as a fairy does. Her whole body should be wreathed in flame. Her hair should be down and any clothes she is wearing should be formed from the fire since her other clothes will have been burned away. This "fire" is an extension of herself, so you can play with that idea if you want to. She should be the same height as normal.
I'm giving everyone creative leave on this form. All I care about is that it looks like Raethi. Take or leave the wings if you wish, but have fun with it ^w^.