Play with herself.

"Play with your nipples," you suggest.

"What? I would never! Even under the influence of sorcery I wouldn't dream of doing something so... aah! No! What are my hands doing! Stop!"

Her face is glowing as she gently teases her small, coffee-coloured nipples, rubbing them in circles, stroking them and flicking them back and forth. She can't stop herself from letting out a small moan. In no time at all they're hard, aroused into stiffness.

"Now stroke your clit for me. Tell me how much you like it."

"You fiend! You bully! Don't you dare... oh, I like it, I like it!" She runs her nimble fingers through her dark nether curls, finding her sweetest spot and gently stimulating herself, just the way she must do when she's alone in her sleeping bag at night. She hangs her head in shame, unable to meet anyone's gaze, as a hooting crowd of city-dwelling rubes watches her engage in this deeply private and personal pastime. "I love it! I love to play with myself! It makes me feel wonderful, you bastard!"

"Keep going until you're about to cum, then stop." You smile as you watch her fingers probe deeper into her pussy, and her whole body vibrate with pleasure and humiliation. Highly enjoyable. What else could you have her do?