In my opinion the bare boob does distract me more than it adds to the picture. You may consider a bra or something to emphasize the body line but hide the obvious? Other than that, a beautiful model and a wonderful sight
The nipple is necessary to keep the viewers eye in the photo for a longer period of time. For me: The eye sees the face, gravitates to the nipple, studies the nipple, follows the fabrics, examines the beauty of the face, appreciates the whole. Cover the nipple and the photo is unbalanced and the eye spends much less time in the photo.