Stella is one of the Eldar.
She alone is specifically described as eternally young in a land where, unlike Baum's Oz, humans do age. And unlike all other characters in the series, she speaks in a lofty and flowery manner appropriate for the Eldar. And finally, her reaction to being given a source of power is to remove it from the world to prevent it from being used for ill purpose ever again; how very Tolkienian!
