While it is a good piece, her lipstick could be better, and while her facial expression is nice, a slightly more open expression could do wonders. Try and get your model to connect with the camera- she has a great mysterious expression, but a little more oomph around the eyes would take this from a good picture to an amazing picture. Also, make sure she uses lipbalm below her lipstick.
I love how you focused the image- the soft background beneath the sharp focus in her face makes the image quite striking, and the purple-gray unfocus brings out the purple tones in her eyes. (Are they color contacts or does she just have amazingly colored eyes? Either way, the background is perfect for them.)
Overall, it's a lovely image of a lovely girl in lovely clothing, and I thank you (and her) for brightening my day with it.
I know you are looking for comments that would help you improve, but I don't think this image could improve. It really is top notch: looks professionally done, has a clear theme in mind, and is executed properly. Model's facial expression fits the theme, the lighting is sound, and the focus is right where I feel it needs to be. (As the viewer I'm allowed to say those kinds of things. )