Sophie hasn't had a proper tickling session yet, so I'd like to concentrate on her. Since she's a cowgirl, I was compelled to consider her natural nemesis... an Indian antagonist! They always have plenty of feathers handy, after all. I was thinking in terms of a sawed-off type, sort of an native American version of Rosie's old foe, Damien. He could have an intimidating Mohawk haircut and scary striped war-paint. Of course, an Indian girl could be just as much fun (plenty of beads and buckskin clothing)! I see Sophie staked outdoors in a sitting position, her legs separated and her feet fixed by thongs. Her cowboy boots could be propped nearby (perhaps only one bare foot, for contrast's sake), as her tormentor lounges, delivering achingly deliberate torment to her poor defenseless sole!
I know, of course, that distinct ethnic types are chancy subject matter, but I have seen Indians used in past tickling pictures. Barring that, how about some sort of animal opponent? Coyotes, buzzards (feathers again), burros, lizards... they're all recognizable Western iconography. How about an anthropomorphized Gila Monster? He'd be great fun to draw, what with the multi-colored beaded skin!
Well, those are some initial thoughts. I'd be interested to hear what other have to say along these lines. I'll bet there's something basic I've neglected. Once again, great idea Pab! You sure know how to keep the fans interested!