I like the composition, but the above poster does have a point, because there isn't too much going on in the background that needs attention.
You captured a great smile, she looks lovely. Keep in mind to check the little things before shooting a portrait. The clasp of her necklace is hanging down in front, and that could have been fixed if you'd noticed. I also think the photo looks a little washed out, perhaps a bit more saturation and contrast? What post processing did you do on it?
I'm not a fan of the colors of the hat and shirt, they don't seem to go together right. IMO this shot would look better in black and white. (Although I know I'm contradicting my saturation suggesting).
Overall you did a good job for your first portrait! Keep it up =)