I've started on my CS for my Miss Marvel character, Caroline. I've gone ahead and put what I have for her so far in my characters post. My basic concept for her is that she is very powerful, but lacking in the maturity, martial arts experience, intelligence, etc. of the older members of the cast. I don't think that I'd want to introduce her until after the main group has had a couple of missions/public fights. She'll start trying to be a fairly traditional superhero-type. Because of her raw strength, she is way overconfident in her abilities, and a few solo victories will really cement that. I figure that she wouldn't join up with the team right away until a situation (probably getting her ass handed to her, and saved by the team) makes her realize that she can't do it alone.
Also, I thought that her parents could be the owners of Sammy's Hardware Store, through which she'd know Luke.
But anyway, that's just what I have for her for now. I figure that she'd make a couple of cameos, getting active in her hero-escapades as the team assembles, but only be properly introduced later.