Overall, you did a really nice job. Especially considering you're not used to drawing people? So what I'm about to point out are details and things to keep in mind about consistency.

What I like: your anatomy is good, your shading is good, and her likeness is impressive. I know it's very hard to draw an actual person and make it convincing. You do that especially well with the pose. And, obviously her hair and outfit, but she'd be much less recognizable if she were in a strange pose. I also like her eyes and how you drew the jewellry. Speaking of which, you did an awesome job with the clothing.

Now, for the details. Her lips are not entirely convincing. They're a little wider on one side and a bit distracting when you focus on her face because you can't tell if she's smirking or smiling. The shape of her face is also a little skewed. There should be a little bit less of it showing on the right side...more shadow. Hats off to you for the nose...nice job. Her left eyebrow seems to be coming way down and is sticking out a little? Also, her right eye should be a teeny bit closer to the left one for better balance of her features. But really, the one that throws the face off the most is the lips. I like the hair, I'm sure it was time-consuming.

The skin on her belly should be smoother, less textured because it's blending in too much with the texture of the fabric. Her hands are good, though her fingers seem a little short compared to her arms, and the shading is a little flat.

The things I've mentioned above are hard to see while you're working on a piece, and even right after you're done. I find that the best thing to do to fix that is to just leave the piece alone for a few hours, and then you can come back to it with fresh eyes. That way you can see the things you've missed and the things that are off.

Now for the background and consistency. It really bothers me that you didn't shade the space inside of her arms at all and that you left a white outline around her body, even though you shaded everything else (almost). But the darkest part of the background is still strangely floating around (and in the shape of) her outline. It looks very unnatural.

There is such a contrast between the intricate shading of her figure and the background that the background appears very sloppy, and therefore detracts from the whole piece.

I hope I wasn't too harsh. I honestly want my critique to help you. I really hope it does. And I know (from your artist comment) that you didn't have much time for this. I'm sure that was the cause of most of these oversights, because you obviously have a lot of talent. I really admire what you did here. I bet your next person piece will be twice as good. Best of luck.