Lady Macbeth's intent in saying that they must not dwell on the murder of Duncan can be interpreted as her concern that if they linger on the act and its moral implications, it will drive them to madness. This indicates that she prioritizes their ambition and desire for power over the psychological consequences of their actions. Therefore, the most fitting interpretation among the responses would be:
She's afraid they will be caught if they do not quickly move on from the act.
This reflects her urgency to put the murder behind them and focus on their ascent to power, implying that dwelling on their crime could lead to paranoia and potentially being discovered.