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I'm getting really frustrated with this drawing now. I just want to get it finished!
I know that just a bit of shading here and there should do it....but, I just can't get the shading right..... I haven't asked if I can show this person's photo on the web so I'll just show the area's I'm having problems with.
As far as I can see I think you have the nose a little flat. The shadows on both sides seem to be identcal and suggest that the slope is identical too. But I think you'll find there is a much harder line to the right (our right) with a stronger shadow - you are losing the sense of there being a protruding ridge.
I marked the edge below and also....
...at the base of the nose - if you look very carefully I think you can just make out a curved line curving up from the right nostril? This delineates the edge of the rounded tip to the nose. Your drawing seems to imply that we are looking at the nose straight on. But we aren't - the face is slightly turned to out right.
Oh Boy..... this is easier to see than to decribe!!! 
Great job with the hair! 
MIKE
www.SibleyFineArt.com
www.Starving-Artists.net