This is an intriguing photograph. I was struck by a couple of things. First, the magazine's pages are larger than those of the typical American comic book. Second, the images appear "three dimensional"--that is, they seem to be photographs or fully-painted illustrations. This leads me to wonder if this could be one of those Italian graphic magazines which later evolved into the photo-novels Americans call "fumetti" (in Italian the word refers to comics in general).
Here's a link to a site about Walter Molino.
http://www.liceoberchet.it/storia/waltermolino1915-1997/grandhotel.html He was a talented and prolific Italian illustrator/comic artist. It shows pages from "Grand Hotel," an Italian weekly featuring serialized romance stories painted in a photo-realistic style. "Grand Hotel" was active during the late 1940s . I've seen examples from 1947. So I'm wondering...
Could the woman be holding a similar magazine? Italian and French magazines could have found their way to Mississippi via New Orleans. It's hard to tell, but her magazine appears to be a Western. All the photo-real comics I've seen have been romances, but I suppose there could have been Westerns too.
Another possibility is that this is a photo-novel adaptations of a movie. I have a couple early Italian examples. The panels are frame blowups from the movie with pasted-over balloons. However the ones I have date from the early 1950s and I'm not sure movie photo-comics were published as early as 1947.
It's conceivable that Frenchman Cartier-Bresson may have brought the magazine with him to the shoot. It wouldn't be the first time a photo-journalist provided a subject with a prop. It's all very interesting.