A. It helps the reader understand the implication of events better than the narrator could.
Explanation:
By definition, dramatic irony is the phenomenon of the reader knowing more about the reality of the matter than the characters themselves.
This literary technique in especially useful in works with unreliable narrators because it gives the reader the opportunity to know and understand the plot of the story independently of the narrator's words. In other words, the reader does not need to rely on the characters to understand the events of the work, thus being able to detect unreliability, where present.
You can that aunt marry is someone who is very nervous and cautious by how the author used the word shrieked and how you can infer she was scared by the tone of the story