Wow, this took longer to get around to than I thought. I was never able to get quite the right angle in-game, but I recently learned that Portal 2 maps can be imported into Source Filmmaker, which lets me do fancy things like cut out foreground objects (like this railing) and place them on another layer, and mask grated floors for shadows. DasMatze's green screen panels made the job a lot quicker.

Fuchsia's version of the turret costume was inspired by swimsuits from the 1980s, when absurdly high leg lines were apparently all the rage. I did a second render with an actual turret model where she's standing to sample color levels; I didn't realize how friggin' dark this area was! Good thing this site has a dark background...

EDIT: Oh fuck me, I'd forgotten that the actual game has HDR, so I was getting too dark of an image because I hadn't adjusted the camera's exposure. I went back and re-rendered the scene and the color samples and rebuilt the image from that. It's a lot more visible now.