It looks very pretty. If you want to define the neck and chest more I'd say; don't hesitate to go for bolder shadows. The hair is light-colored, yet you still use a few dark shadows here and there; nothing is stopping you from doing the same thing to certain areas of the skin.
It might also make it look more natural, if that's what you are after, because the underside of the nose and the neck are generally - depending on the lighting of course - the places on and around the head that catch a lot of shadow.
I get that you are going for a very clean style, so defining the muscles and tendons in the neck more might not work very well for this piece, but at the same time it could also be worth a shot. When one is relaxed, especially someone with little muscle mass, there isn't all that much definition going on in the neck, but some vague hints are still likely to be present.
Hope this helps.