Okay, here's what I came up with.
I went with the rules and used my imagination based on the small amount of information I was allowed. She told me that this was a character that started out good, but may have the good/bad line blur a bit later, so I designed her with a darker outfit, while keeping her features and expression relatively "good-guy-ish."
The referance I used for this design was just the latest designs. so I tryed to maintain some harmony with those charas, (makeing her look like she belongs in the same story with them) while still being unique and recognizable.

I left the design without any elements such as jewelry, weapons, etc. as I don't know the story or the character's background enough, and such items often carry a storyline-significance in character designs.

Now that I look at her, my main concern is whether she ment crimson red hair, or more natural red hair like I've got here.

She's all yours now, *bows*