Wow, I love this picture. The girl is sweet and has a perfect body; an example of feminine beauty. On the other hand, she it a bit to "soft" for an assassin; maybe you should add some scars, or at least some dirt / dust on her skin, and a more fierce or focused expression on her face.
I really like the outfit; it is creative and a nice example of the "warrior girl" attire in fantasy art. Although revealing, it is not inappropriate; rather practical, allowing for swift and silent movement. The arm and leg protectors are a nice and creative addition, and the bare feet make her look cute and innocent, an interesting contrast with her profession.
The background is nice, and the composition of the picture is good. Overall, great work, and an instant fav. Keep it up!