I think Mari looks great! for shading, I'd use some references, pictures that you find that exhibit the same kind of lighting as you are looking for. A master example of someone working with single sources of light is Caravaggio.
keep in mind where your light source is, in this case the strongest source will be the flame in her palm. think about how that light lands on and reflects off of every surface. With Mari's armor, you can have a lot of fun with reflections. maybe some torches on the background walls and whatever ambient light there is. take some snapshots in the sewer for references on perspective and textures.