Really can't add to Steven's thoroughly informative critiques, but would like to share what I do at the photography review.
I edit all my photos before showing the client. I take out any photos that would absolutely, positively, NOT work as a painting. In addition, I choose 2-3 of my favorites from this selection to do as a pencil sketch, in proportion to the final piece. These may be a combo of several photos. That way, the client will understand there is a difference between a good shot as a photo, and a good piece of reference for a painting that may a summary of several.
I do like your portrait. The colors are clean, fresh, and I get a good sense of her personality. Nice job on this one, watch the harshness of edges on the next one.