Desert Rangers are now NCR Rangers, but not all NCR Rangers were once Desert Rangers. Also, I'm talking about the ones from Wasteland. Hell Razor, Angela Deth, Thrasher, and Snake Vargas are the epitome of Ranger-ness.
I'm assuming this is a flashback to a Nightmare Night from their fillyhood, in which case I like the subtle (and subtly emotional) explanation for where AJ got her hat, and why she's so attached to it.
Or maybe I'm just a horrible jerk that doesn't care for the show's canon and implements my own version of things into pictures! Or maybe Applejack never got the memo of her father's death and has been laboring under the assumption that her pappy went to get smokes several years ago and got lost on the way back! Or maybe the magic of art lies in its ability to tell several stories at once, and the only true meaning to the piece is that which the viewer gives to it, and everyone will interpret this piece in their own way! . . . . (or maybe they're just fillies)