Edited the creases, added highlight on left side and darkened area around crease on right. Added a little white to her teeth which were a little lackluster. Toyed with ambient lighting to make a little more noticable. Edited cheek to nose transition on dark side.
Things the edit didn't adress because I'm lazy
-Her neck is stil too small across. When I tried to make the proportion more realistic, she assumed the muscleman neck, and I realized her neck was a bit too long. Try to shorten and widen it.
-The seperation of a real smile from a fake one is the eyes. Right now, the smile doesn't seem to affect her eyes, and what she has now opticaly would look more fitting to a straightlipped expression. Look at your smiling reference. She alsmot assumes the anime style ^_^ thing. Don't really do that, but a real smile will narrow your eyes a bit.
Her hair isn't very thick right now, it seems to be hanging from her scalp very sparesly. I like the outline of hairs and on the shoudlers, but combine that with the original thickness you had, it will make her look more healthy.
Keep it up, Ter.