Sonia's Birthday Present

Lighten the whites of her eyes, usually people's teeth are the same color or darker than the whites of their eyes. You might be trying to keep the focus on her smile but it looks a tad unnatural to have this much of a difference.

The hair looks good, but I'd add more on the bottom to make it look a little less piecey and a bit more realistic.

The part of the hair should be lighter, not darker, because her skin is going to show a little bit i.e. [link]

If you don't show any skin at all it gives a bit of a wig-like effect.

The eyebrows have too much three-dimensionality, especially the left one. Eyebrows are made up of a lot of little pieces of hair that lie relatively flat against the skin, and they're usually pretty uniform in color--it's their variable density in front of the background of the skin that makes them look darker or lighter.
[link]

Let me know if you have questions about this. It's pretty damn good, keep working and good luck!