Reasons this fell short, hmm, I think shooting this with a longer lens would have been a good start. This would compress her featrues a bit, as is her head seems pretty large compared to her body. The brightest spot, or at least largest is right on her chest, this draws attention away from what should be the focus, her face. Just a couple thoughts
Hmmmmm. Maybe if the dress, lip color, eye shadow and background complemented or contrasted each other more strongely I would like this image more. Still a good shot.
Is "Deep Purple" the subject matter we should be interested in here? Your model is very attractive and doesn't need the "sex sells" approach IMO. You've done a very nice job with lighting and all technical aspects of this challenge entry. Good luck.
Including her legs and hand in such a fragmented way weakened what I think is a fabulous portrait. I would maybe have cropped 1/2 way up into her right breast.