Making Beth cum

You've taped Beth's ankles together, put her in cuffs, handed her a wand vibrator and make her masturbate. She claims the vibrator isn't powerful enough to do anything for her, but you insist she continue for 2-minutes, and after a few seconds, Beth admits that it feels pretty good. She begins to squirm and actually looks like she's enjoying it. After a minute or so, Beth confesses that it feels very good and she starts begging you to let her stop. But you're in charge and make her keep going much, much longer than the 2-minutes you said several minutes ago. It all proves too much for her after 10-minutes. After she cums, she tells you, "You win!"