I'm not an expert but from my understanding an image, or more precisely, a part of an image, is overexposed when you lose detail that should be there. Your histogram will help but it is the printed, or published (web) image that you are concerned with. In your portrait the area between the models' right eye and ear is overexposed because it lost noticeable detail. The same with her right hand, if you look at the joint for her thumb the bottom of the hand shows the crease in her skin but you lose that when you get just a little higher. Looking at her cheekbones you will notice the subtle contours of her left cheekbone but some of that is lost on the right.
With all that said, it doesn't make it a bad image. It will get picked apart on here sometimes but you see it in magazines and ads all the time, done by high dollar professional photographers. To me this is a great image and I wouldn't change a thing. Probably about 1\3 stop less on your camera left light would have made a difference if you want "by the book" perfect.