Backlit

Ok, now that I've had time to pick my dang jaw up off the floor maybe I can start actually giving you a somewhat useful critique.

As I said in the comments, this picture is absolutely stunning. Everything from the straw hanging in her lips (almost as if she has forgotten that it is there) to the deep and contemplating expression on her face is so subtly powerful. It is clear that you started this portrait with a very clear intent. The decision to put her iconic hat deep, yet omnipresent in the background instead of on her head seems to be indicating that she is thinking about the hat itself (as though it is a symbol with some great meaning for her).

I'm afraid that the subject matter is far from very original so I can't, in good conscience, give very many points for that. However, that isn't really too important to me. Topics only become common if they are worth talking about and art is no exception.

As for the technique, I'm afraid that I am not the best drawer in the world so it is exceptionally easy to impress me after an artist reaches a certain skill level (and you are well into that it seems). Therefore I must instead judge your technique on your attention to detail and accuracy to the character of Applejack.
I feel that her ear looks a tad off to me. It seems too large and not nearly as powerful and solid as the rest of her (sort of like you drew all of the rest of her with a perfect mental image of what you were going for, but as soon as you got to her ear, you didn't know what to do with it). It's not terrible by any means, it just doesn't hold a candle to the rest of her perfect, powerful features which makes it really stick out.
I LOVE the muscles in her jaw and neck. They are gorgeous.
I had to take another point away for failing to remember her freckles. It's not a huge deal, but they are very iconic facial features that are unique to AJ.

All in all, this is a wonderful portrait and I am honored that you've chosen to share it with us. I have every intention of watching you from now on if I am not already doing so, and you can bet that this is going up on my desk top for a few months. For everyone's sake, keep drawing and creating your art.
Well done.