Yep, I agree. When I first looked at the images I thought, "There isn't that much fog/mist in the whole world!" Then I saw the obvious processing signs -- which is NOT to say it distracts. Lovely images.
I think you will find it is a simple Gaussian blur in a U shape to include the foreground and into the background either side of the subjects, probably done as a brush (good), a layer mask (better), or a grad layer mask (best), it's what adds to their isolation and that "unique look" that the 135 is supposed to have. Funny, with decent post skills any lens can have a "unique look".
Well, it seems there is an obvious trait of this image that is not being discussed. The vignetting (likely added in post as "post crop" vignetting...yes the 135 f/2 does vignette wide open, but not nearly this much). But the vignetting serves to spotlight (and almost 'bulls-eye') the subjects, making it that much more of a "portrait".
This technique is really not all that unusual, anyone can do it. Not saying it's not a nice image, certainly it is. But it's really more the lighting on the subject(s) (and the darker light surrounding it) relative to that darker background bokeh, that make this image successful. The bokeh alone (whether natural or 'enhanced'), is not what jumps out as a primary feature of this image. The spotlighted subjects are what jump out, from against the dark. That's how I see it anyway.
I have nothing against doing any of these things to an image in post. But it's important to point out that these are not 'native' features of the lens alone. What the photographer has done here, serves to exaggerate the features and even 'artifacts' of fast prime lenses (to a pleasing result)...and in this image it works fine. But anyone who has edited images for a while can easily see the image does not look like this straight out of the camera (especially if you have the camera set to compensate for vignetting in the first place...Which is usually the best way to do it, because that way the photogorapher/editer/artist can choose how much and where, and whether or not to apply any...vignetting in post).
+1. I love what I've seen of her work. Elena has a definite talent and eye for portraiture and I am quite sure that she shoots for the edits that she wants make. Elena really nails her subject and ambient exposure which enables her to create such powerful images. Her post-production techniques highlights her abilities and are not being used as a substitute to good photographic technique.
Eos: 1Ds-III, 5D-III, 6D, 60D | Canon EF: TSE-24L-II, 16-35L-II, 24L-II, 35L, 40STM, 100f/2.8, 135L | Wishlist: TSE-17L, 200f/2L
Tamron: 24-70VC, 70-200VC, 150-600VC | Samyang: 8mm-T3.8, 14mm-T3.1
Crazy Ideas: TSE-90L-II, 40f/1, 100f/1.4, 35-85f/2, 100-300f/4_1.4xInt, 500f/5.6_1.4xInt