I am quite impressed with your work here. The eyes are great, the lighting is fantastic, and the little touches with the bottle and the sword really pull it together. Now for some comments:
 The shadow of her back leg, right in the center on the ground, seems a little bit off. Maybe skew it more.
 The angle of the arm that is holding the sword seems slightly awkward. It probably would have been better to have her resting her arm on the armrest, possibly holding the sword by the crosstree instead of the hilt. A much more casual feel.
 The wood texturing on the throne seems...simplistic. I'm reaching here, but it seems like it's not quite gritty enough, or it's too uniform. It might be the sharp black gaps between the pieces.
 I was under the impression that the Scout-pattern legs (the original ones) were white, to match her coat. Not that important though.
On the whole, this is a very solid piece. Everything focuses the viewer's attention squarely on Blackjack's face, but there is plenty of extra detail to stare at. ALL HAIL QUEEN WHISKEY!
...Okay, only now do I find out she's not a stallion. I was similarly confused at the beginning of FoE regarding Littlepip... and at the beginning of MLP:FIM regarding Applejack... I really need to start reading "Project Horizons".