I love, love, LOVE the fact that she's wearing the same basic armour style as the men (well, I assume they're men; can't really tell) instead of something that conforms to the shape of her breasts! Such "boob-breastplates" are a popular style in fantasy art, but they would have been absolutely terrible in actual combat (especially the kind where all the character wears is a platemail bikini, leaving the rest of her skin uncovered).
She looks like one of the Clayre, from Garth Nix's Old Kingdom series. The Clayre are blonde women who live in a fortress in the glacier. They see the future, and take care of themselves. There is a Captain of the Guard who is mentioned several times in the 2nd book (Lirael) so I thought it was meant to be her until I read some of the comments.