In "The Open Window," why does Vera ask Mr Nuttel if he knows her aunt?

Vera, for whom
"[R]omance at short notice was her specialty," asks Mr. Framton Nuttel if he knows her
aunt so that she can determine the design of her forthcoming fabrication. Having perceived that
Mr. Nuttel is unprepossessing, nervous, timid, and unstable, Vera knows after asking Nuttel if
he is acquainted with her aunt, and he says he is not, that she can create an outlandish tale
for this shaky and gullible man and he will be terrified by it. For, she is cognizant that she
can lie about  her cousin and uncle and Nuttel will believe her.

So, then,
after having told Nuttel that her aunt is not mentally stable and imagines that her deceased
husband and son will return from their hunting trip, Vera continues her lies by embellishing the
effect by creating the tone of absolute surprise when Mr. Sappleton and his son return and enter
through the window, a tone which engenders the terror of Framton Nuttel:

The child was staring out through the open window with dazed horror
in her eye. In a chill shock of nameless fear, Framton swung round in his seat and looked in the
same direction.

So terrified is Nuttel by this blurring
of the lines between reality and imagination that he grabs his hat and cane and charges out of
the house.