The pixel has a decent light source going on, however some areas have pillow shading which doesn't look all that good, personally.
I dunno how to say it, but in some areas in the pixel have multiple of similar shades, you'd be breaking coloring limits if you kept those, that might be something in SAI though, also consider adding a darker tone to the lines in the back of the hair, it'll make it stand out more.
Otherwise, the rest is good!