The "twist" of this character is that, for as long as possible, I would keep her origin and true nature ambiguous. I'm thinking back to the way Mark Millar originally wrote Ultimate Thor, in that she claims to be an actual angel, from Heaven, but most people just assume that she is some kind of super-human and the whole "Angel" thing is just an act.
So is she really an Angel or not?
Honestly, I haven't figured that out yet. But I'm thinking that in an ongoing series it could be fun to drop hints and leave that for the readers to decide.
This awesome image is from the Sensational Celina Hernandez.