Whatever its range, it would seem to draw a lot of power. Marlena only used it three times before walking out and letting Kirk deal with Sulu on his own. This suggests that even with a warp-driven ship the device would need to be "re-charged" after only a few times.
Or maybe she knew that once she'd made the odds more even, Kirk could handle the rest himself. Maybe she figured that if he couldn't take Sulu down himself, she was backing the wrong horse, so she left him the opportunity to prove his worth.
Or maybe she was late for her manicurist appointment.