I find the hues used here to be interesting. Hoping that I'm right that this is a pen drawing, it's not a plain pen drawing done with just blue ink but with a touch of purple to get the highlights of her hair done. While this piece may be overshadowed by other pieces done in media with a wider range of colors, this seems great for a pen drawing. Either that or I haven't surrounded myself with enough awesome pen drawings.
When I think of Twilight, there's definitely the nerdy side of her, but I also see her as a bit active she sometimes dive into things whether it's confronting enormous monsters or in general blasting away a bunch of baddies. The schoolgirl look seems very typical for a lot of human adaptations of this character, but it makes me wonder if it's possible to have a set of clothes that has both the nerdy and adventurously daring side of her. Well... maybe you have daring in the sexual sense, maybe. (lolminiskirts)
Makes me wonder... is she the sort who wears jewelry? I would imagine girls who wear jewelry to be the girlier types to be concerned about their looks, but Twilight doesn't seem to be much for that.
I haven't paid too closely to human anatomy lately so I won't be able to catch too many things, except maybe the face being slightly off. I know it's stylized and all, but I noticed if I were to imagine an imaginary line running down the middle of her face, the line wouldn't end on the point of the chin. Again, coming from somebody who hasn't paid too closely to human anatomy.
I dunno if people see the same thing, but the straight lines used on the jacket seems to convey an evenly flat area but we know that it's not really the right shape. While it's probably already pretty difficult to have neat curvy lines here instead (not that my own motor skills would do me much justice), it's just a little something I notice that seems a bit funny.
Overall, this isn't bad at all, but any more little bits of insight that could potentially be offered here, I'm not able to offer much more.