Lovely. My reaction when I look at this is, "I want to meet her - I wonder who she is? She looks like someone worth knowing." It's a picture of a person, not just a face. I would try for some constructive criticism, but there's nothing here that I don't like.
So realistic, beautiful in every way. I love that its so photo realistic but it still /looks/ like a painting. You kept to a style that was your own instead of a general photo. The lighting is wonderful and the shading is too. The only thing I'd have to pick out is the background, with such detail and time into the person there is a massive lack in background which makes it appear like shes standing in front of a green-screen. Other than that I love the look and emotion of contentful happiness in this young woman's eyes.