While option C is a reasonable interpretation, the most accurate answer based on Lady Macbeth's lines in this context is A. She does not consider the murder to be a subject worthy of considerable thought.
Lady Macbeth's insistence that they must not think too deeply about their actions suggests that she views the murder as a necessary means to an end rather than something that should weigh heavily on their minds. This aligns with her character as someone who is pragmatic and focused on ambition rather than the moral implications of their actions.
Option C implies a fear of getting caught, which is not explicitly supported by the lines provided. Lady Macbeth's primary concern in this moment seems to be about maintaining their mental stability and focus on power rather than fear of consequences. Therefore, while your choice could be seen as having some merit, A would be the most fitting interpretation based on the text.