Looks like I might not really be able to do this. I can do some photoshop/gimp work, but it looks like I need to understand NIFskope and the like a bit better first.
Everytime I try to view the nif, it shows up as the model with a blank texture.
I can, however, offer this advise:
-Make the entirety of the skin besides the finished breast part closer to the shade on the light spot of her neck. Close, but not exactly. Leave it just a bit darker. Just slightly. Just take the eyedropper, select the lightest part of her neck texture, go to paintbrush, set it to maybe 15% opacity, and just keep going over those areas until they're somewhat close in shade.
-For the lower half of the breasts (which is currently missing), simply copy the finished half, flip it upside down, then use clone stamp and smudge to even it out.
That should leave her looking a lot better.