First I flipped the original, copied that layer, and desaturated one of them, messed with the saturation and contrast until I got a good BW look then added a smart blur
step 2 of 4
Went to the colored layer and extracted the hair, eyes, and lips either keeping the color or enhancing according to little more than whim.
step 3 of 4
Copied half her face with the polyogonal lasso making sure the selection bifurcated her teeth. Simple copy and paste into a new layer, then flipped that layer.
step 4 of 4
Matched the new layer up using the lips and teeth as a guide. Then did a little working on the seams between the two so that they blended well. Then I worked on a few wrinkles, tweaked the contrast, levels, curves, and saturation, and put the hair, lips, and eyes on top for some color.
Finally I merged the layers and rotated them to an angle I liked. The end result is a near perfectly symetrical face.