Flog her

With a malicious smile, you guide her to the slab in the center of the room. "Stand here while I get something." You walk over to the wall, staying behind her, and pick up a coil of rope and a scourge, then walk back to her. She cooperates - and giggles a tiny bit - as you tie her wrists directly to the hook over her head; it's a bit high, but she obligingly stretches to reach it, standing on her toes, and you manage to tie her wrists firmly in place. You jump lightly off the stone, pick up the scourge (which she still hasn't seen, as far as you can tell, since you've been keeping it behind her back), and strike one hard blow across her back. She jumps and squeals loudly; it's obvious the thin fabric of her top didn't protect her much. You bring your arm back and strike again. And again. And again.