Allow me to be the first one to comment on your art! As someone who does both traditional and digital, I gotta say that this is pretty good. The design is done in a way that still very much encapsulates the original looks of Cass but puts a little bit of a spin on her, which is nice to see every now and again since people can go pretty ham on redesigns. I also absolutely love the way you draw the gun! I never put much detail on 'em for times sake but the way you drew it so clean and precise.
Now with every piece of art, there is always room for improvement. The hand thats holding her book does look a little strange. Her pointer finger is a bit too big and the pinky is just a tad too far from the rest. I also suggest putting one side of the knuckles up higher since it can make her hand look very thin. The hand holding the gun looks wonderful, but she's missing her thumb. I understand it might be behind the handle of it somewhere but it can make it look a bit strange. There's one fold in the over shirt of her left arm that doesn't look quite right. Its all loose fabric there so it'd be best to let it flow down without wrinkles. And then her boob closest to her right arm almost looks like muscle. Though I see how it could be a stylistic choice on your end, its a bit too high up and curved just the right way to make it look like part of an ab.
However, again, there are some very wonderful aspects and details you've put in that these points I've brought up aren't that big of an issue. Just something I wanted to give you feedback on for the future. Keep up on the good work! :]