I like your color sceme. The perspective in the back ground is nice and I like the detail of her costume. Next time I think you should add more detail to the background and use darker shading on the buildings. Overall your art is well done. The proportions are mostly correct. I would also like to see light and dark shading on her hair and her cape.
To the right of the piece where you can see the background under her cape could be more detail and refined. I think you should use darker tones on the background and darker hues of blue to emphasize the lighter tones on her costume from your light source. Hope this helps!