First off, let me say this is a great piece of work, and I really do enjoy this. The colors really set a scene for me, one of a western draw, a duel of sorts. Like she is ready to fight against someone. I'm not sure that was the effect you were going for, but thats the feeling I get, and I do think it is very good color scheme/theme wise. She is dressed somewhat inappropriately in some respects for this scene, however. A strapless (I think?) top is not what I imagine a western lady wearing to a duel, I think of a blue/white shirt with lots of "fluff". This seems to give more of a vegas look to me, and dosen't fit the mood of the picture. The background is also not fitting, in the style sense. It is very well done, don't get me wrong, I love it. However, the colors and style do not match the figure. It seems out of place and not matching, which is why I bring down my vision rating. Going on the positive, for drawing this without reference is nice work, and I commend that. An anatomy book is a good tool to have, I should know, I use one myself sometimes for my work. The technique of coloring is very well done on the character, it all blends well and makes it look realistic. The guns are also well textured, colored nicely and look natural in her hands. However, they do seem too modern, again. The shotgun is a nice feature, but the western draw of the art makes it look out of place. For the handgun, I felt a .357 magnum, Dirty Harry style would have been more appropriate.
In conclusion, you have amazing technique and coloring ability, I think the one thing that needs to be improved upon is the matching of style throughout the whole work of art.
Amazing job overall, very happy with the outcome here (and please go easy on me with this, it is my first critique)