The conflict between Vera and Nuttel is an age-old one: It is that of the predatory, ruthless type against the weaker one.
Vera obviously is a perceptive, mischievous girl because she immediately asks Mr. Nuttel if he knows many of the people who live around there. So, once Nuttel says, "Hardly a soul," the clever and ruthless Vera amuses herself with creating a tale that has enough truth in it to lend it credibility and enough horror to frighten the nervous and intimidated Framton Nuttel.
Stealthily, Vera asks Mr. Nuttel another question in order to ascertain that her fabricated tale of horror will have its intended effect: "Then you know practically nothing about my aunt?" And, when Nuttel replies that he only knows Mrs. Stappleton's name and address, the predatory nature leads Vera to further weave her tale into the "great tragedy" of the loss of Mrs. Stappleton's husband and two younger brothers. This now is a tale that will produce a horrific effect.
Cleverly, then, she continues to frame this story with more details of the truth, blurring the lines between reality and illusion so much that her tale becomes credible to the nervous visitor. Thus, the horrific effect of the supposedly dead men walking through the open window is profound upon the man who has already suffered a mental breakdown.
When Nuttel flees in terror, Vera has won her battle.