This is really cool. You nailed the design really the armor the cloth even the henna (?) tattoo's are hyperdetailed.Everything is killer except the foreshortning on the right arm (for her ) is a little off.
Not that I am by any means better at that , but whay helps me is to draw the foreshortened parts in wireframe, so you can see thru it ( it makes more sense when you do it)
Foreshortning is just really hard and gets easier with lots and lots of practice.
I heard Mangastudio has a mannequin function too.
I use PoseManiacs.com when I can't come up with something or when I am drawing manga ( I am currently working on chapter 1)
For the background , I'd personally would do something like a snowy landscape with smuldring( is that a word lol ) footsteps in it , to show the viewer she packs a power(ful punch)
You will get far if you stay determined , I know you are really good and stuff and u allready came a long way judging by the skill.
Just keep in mind that as an artist you are competing with ''every'' other artist out there.
You have to accpet flaws and embrace them , learn why they are there and baleet the shit out of em.
Learn all those scary things that you can't do (yet) untill you are on a level which satisfies you.
I personally find that I never really know how badly I suck ( I guess everybody has that at some points)
But as an other artist I can tell you that you allready showed that you've got what it takes , the only thing left is determination and lots of hours of drawing.
Respect from a supporter from Holland ^^