Sometimes the second girl's eyes go weird: her right eye goes solid white, and her left eye goes solid red. Also, sometimes she keeps staring at you, only glancing away for half a second, and you lose half a bar of progress…
Perhaps if there were distractions you could trigger, to make her look away, it would add more strategy, and less luck — especially if triggering the distractions in specific orders resulted in different lengths of time (i.e. distraction 1 might be to turn on a TV, distraction 2 might be to knock some bottles on the floor. If you use them on their own, an NPC turns off the TV, and picks up the bottles, but if you trigger the TV while they are sorting out the bottles, then they have to hunt around for the remote control, and it distracts her for longer). Later/harder levels might make it so that she only looks away when distracted…