Disclaimor -- I am in no sense of the word an "expert" or even authority on portraits. Sometimes I get one to look really good, and sometimes I don't. With that in mind, I will simply tell you what works in this for me, and what doesn't. Unfortunately, I can't tell you the *trick* to make this a winning portrait (though I think you are well on your way).
What I think works well here --
Her facial expression is very good, I think. It is somber but reflective, giving the impression that she is a little sad about something. I like how her hair falls naturally and frames the face, without being too distracting, and I think having the flowers out of focus in the front works well because they help to add some color and context to the shot, as well as give it some depth.
What I think is working agains you --
I can only really identify two possibles. To me, there is a yellowish cast on the picture. Perhaps it is an illusion from the flowers, but maybe you could try adjusting the white balance or color balance to see if you could "cool" it down some. Her eyes look like they are a beautiful shade of green, but it is hard to tell with the yellow cast.
Secondly, I think it is cropped just a touch too tight, especially left to right. She feels almost squeezed into the frame.
That said, you have a beautiful model, and have done well here. Oh yeah, I like how the flower and her necklace compliment each other as well.
Good work and best wishes in future challenges.
karmat
I like the composition of your model. I want to push the flowers in the foreground down a bit - they trick my eyes into seeing her skin with a yellowish tone.
Very simple and beautiful. Would have liked it myself a little more if t he flowers in the foreground were just a little lower. I like them there, just maybe not so predominant. (IMHO)
The picture itself is great, awesome lighting, good color, pretty model...I don't care much for the flowers in front...they are a little bit blurred....might have been better if they were not there...not sure how some people are going to take them(flowers)...I try to look at the picture and the main focus..9..!!