Actually the waist is fine it is the shoulders and the bust/rib cage that is where the anatomy is off. It is still very elegant in it's creation. Just widen the shoulders and the ribcage and you should be good!!!
First thing you should fix the waist looks good but i wont fav or anything till that atleast gets redraw or something not to be mean or anything i like it just that waist O.O thats how i looked when i seen the waist lol
Her face is amazing, and it looks as though her waist could be fixed by just making it a little broader to the left, though I don't know how easy that is of course ^^ Your art in general is really brilliant btw. Love it