The revised sentence would be: "Because she left the cabin last, Darcy arrived at the campfire after Shirley." So the correct answer is c. after.
In the given sentence, the preposition "around" is best replaced by "after" to convey the timing of Darcy's arrival at the campfire concerning Shirley. The revised sentence clarifies that Darcy reached the campfire subsequent to Shirley.
This choice emphasizes the sequential order of events and offers a clearer understanding of the temporal relationship. "After" appropriately captures the idea that Darcy's arrival followed Shirley's departure from the cabin, providing a more precise and concise expression of the narrative sequence.
So option C is correct.