I'm not too sure where to pinpoint it, but despite the beauty of its elements, something seems rather off in this painting anatomy-wise. It's somewhere near the head/face and shoulder area. Sorry I can't be any more helpful.
Actually, I'm certainly nowhere near being an expert, but looking at it again I think it's in the width of the shoulders (too narrow) and the consequent twist of the upper body and the placement of the neck. I just really suck at explaining. But I could show you? Only if you're interested of course. I'm aware I'm potentially coming off as annoyingly intrustive.