Finally did that monochrome version of Nadia and I think it has almost worked.
Now that I’ve had some sleep, I can see more of what to do. Her face needs some more light, the shadow on her face needs to be a hair wider from her hairline, and I’m pretty sure it would look better if I put the light color across all of her chest, instead of mimicking the light on the mannequin so closely. (Mannequin is here so that you can see what I’m talking about.)
And while I was doing this, I forgot to paint in the wrinkles of her dress. Looking forward to getting this corrected and finished!