I've never done studio myself so I can't give too much comment on your technique, however in the mod I've uploaded, I've softened the skin slightly, added a glamour glow and removed one of the catch lights, having two in one eye is page 3 lighting and not always flattering for a formal portrait. I've flipped her too as your eye reads across the image left to right, it now stops on the eyes rather than the hair piece. I have also cloned a bit of the armpit out as well as it is quite distracting. I don't agree about her not looking happy, not all portraits need a smile, she looks seductive, which is far more appealing. I've dropped the saturation out on the blue channel to lose the background more as the blue clashes with her dress, I've also lifted her makeup slightly with a hue/sat adjustment layer.
She is a great model and its an interesting shot, you can judge that by the amount of comments, if I could adjust one thing it would be her necklace which doesn't sit right, but otherwise you have the makings of a great image that just needs a few tweaks to perfect it, well done.