At first: You can see, that she really feels happy. The emotion is expressed very well. The picture seems really vivid and dynamic. This is a really great pro - not all photographers can capture such emotions like you have done! Well, i would take a more interesting background - not only black. This would make the picture more shiny and special (: This is a little bit sad ...
But all in all it's a really lovely and beautiful picture. The mood is very great and the girl is very pretty. Maybe you'll take the next time a more colourful background.