Geri says this is a four image HDR shot, so this is my base assumption going in. The halo that Mike mentions is often something seen in HDR images and is a pretty common tell-tale sign. I've done enough HDR work with grads and polarizers to recognize some of the tell-tale signs. Even the anti-ghosting algorithms leave artifacts. The main issue I have is that this is a fairly small image and I can't zoom in to confirm what I think I am seeing.
That being said, the comments I make in my analysis still hold, as these would be apparent in a HDR image. The only place where there might be something that could be hidden, that might be the GND use, but I would expect to see some artifacts from the tone mapping process where the rocks and sky meet, especially if she used a hard grad on the horizon, but I don't see any, so I suspect my analysis is still likely correct. I've had to go an clone out some of the transitions from using GNDs in my some work; the tone mapping process can't tell the difference.
This shot uses a polarizer + 5-stop ND and is HDRI, The sun is camera left and close to 90 degrees off the optical axis:
Halos in an HDRI shot anyone?