Why does Framton think that Mrs. Sappleton is mad?

Framton Nuttel thinks
that Mrs. Sappleton is mad because he believes the totally fictitious story that her niece,
Vera, tells him about dead relatives and her aunt's refusal to accept the deaths. Once Vera
learns that Framton does not know her aunt at all, she concocts a story of ain which her aunt's
husband and brothers went out shooting and drowned in the bog. Vera explains that her aunt
"'always thinks that they will come back some day ... and walk in at that window just as
they used to do." She tells Framton that this is why the big window is left open even on an
October afternoon. When Mrs. Sappleton enters, she explains that her husband and brothers are
expected home soon, and her eyes continue to stray away from him and toward the window. He finds
her apparent inability to move on from this tragedy and her insistence on talking about it quite
"ghastly" and he tries to change the subject.