Natasha let me have her thoughts on my WIP. She was a little concerned about the virtical indented area between her nose and mouth, which she felt was too pronounced. She didn't know what it was called, and neither did I, which is simply not good enough for a portrait painter! So I looked it up and it is called the PHILTRUM - a new word for my portrait painter's dictionary.
Anyway, I hope I can convince Natasha that my depiction of her is reasonably correct in this respect. It was the strong shadow thrown from her nose, rather than the philtrum itself which was causing the problem, and I hadn't painted the underside of her nose at that stage. So here is the updated WIP. I hope Natasha's features look a little clearer now. It's not quite right yet - but progressing in the right direction.