The image looks like it could have been done in-camera, if the camera had a multiple exposure function. If the camera was tilted down for the first exposure, level for the middle exposure then tilted up for the last, you would achieve the stepped gradient effect we see here.
The model looks to have been photographed against an evening sky (or sunset), and appears as more of a silhouette in the first two exposures (where she "appears" top and centre), which is what you would expect if you didn't have any fill-flash or other light source to illuminate the model.
If the first two exposures were handheld at a relatively low shutter speed, a flash firing on the last exposure would explain the crispness of the model at the bottom of the frame.
I'm not saying this is how it was done (obviously I'm not the original photographer) but it could have been done in this way without the need for any darkroom trickery.