I see alot of effort here and cool ideas, good job!
I allowed myself to do an overpaint of your latest wip, mainly checking the values and pushing the face rendering ^^.
I see you have improved with the 'shinies' now I would try to make it seem realistic with lighting and shadow areas, like the Nose area with the extreme highlight and general Shading. Also when painting faces think about how the eyes etc. would fit into a skull, using refrence is nothing to be ashamed of Dont be afraid to go into really dark shadows here, her hair pretty much covers alot of potentional lighting here.
yea, mainly touched up the face a bit ( didnt want to like ruin your style, but maybe try some real life anatomy work some more