In my opinion the gradation of light to shadow from left to right matches the outdoors to indoors transition. She is out the window and as you get more out of the window you will naturally have more light and as you get closer to inside it will be a bit darker.

I think that using photoshop to manipulate a photo isn't out of the norm since I regularly will import a scanned image to photoshop rather than use the software that came with the scanner or will just drag and drop a picture from my camera in to PS to crop it, reduce it's size, etc. If it's from a raw file I will surely have to convert it in some app so it's going to get manipulated in something like lightroom or whatever. I'm sure many others are the same.

I agree that it certainly could be faked, but it's pretty well done if it is and couldn't say with any certainty this one is.