Well; the big thing is, she wouldn't be a part of the group. At least not in the sense that she chose it...

My idea for her is that she's young, sweet, bubbly... and blind. First idea is she went out with her older brother to explore one of the smaller not really talked about islands, and something went wrong, either got separated or plane went down, or something attacked them, and now she's left alone and scared trying to find him again (days, weeks, months, who knows).

The second idea for her was a found alone on a yach, last one there after a storm, separated from her family.