That was one hell of a look into Scale's situation there KAM, good going!
Without having gone through availbale thropes myself, I would say that Plucky Girl
might be the most fitting for Scale. She has moments of selfdoubt as well as being depressive at times, but despite this she still fights on, not giving up and not standing down, especially if the lives of friends are at stake...
I do not particular fond of "Chosen Ones" and "Prophecies" in storylines myself. I can, at most, accept the sudden "You were the Chosen One!?" at the end of the story when everything suddenly comes together and what wasn't appearent to the reader until then, suddenly becomes clear... but reading the story all the way and knowing the hero is the Chosen One, or just that there is one, takes something out of the story.
I guess you can't add Unchosen to Scale as she didn't go with or against any destiny, she just did what she had to do, following her own ideals.