Textures are the most important factor to the final realistic girl. There are many high resolution human photos and textures on this website www.3d.sk - I selected a photo from here for my girl’s skin.
These are the textures that I have composed in Photoshop from the photos.
Shading tips:
I use ‘mental ray fast skin sss’ to shade the girl’s skin. The shading network is shown below. I used almost the default setting of ‘fast skin sss’, but I still created some delicate effects with it, such as colourmap will turn to grey on the edge. Also, the bump value will turn to a high value on the part facing the strong light. Facing ratio can also create a fake ‘fuzz’ effect.