Three days later, Seth wanders up the front drive singing "Shenandoah" in his wraith of a baritone. The house looks as it did in the first act of "Homecoming." Seth peers at the flower garden and notes that Lavinia is picking flowers again like Christine would. She has already filled the house with them.
Lavinia appears dressed in deep mourning, sleepless and haggard anew. She gives Seth a bunch of flowers and emptily orders him to keep them to the maid, since the house must be cheerful for Peter. Seth coaxingly offers to haul out a sofa so she can sleep. Lavinia declines and then pauses; Seth knows that there can be no rest in that house. Seth urges her to go away. Lavinia resolves anew to flee with Peter and let the house rot. He moves off and greets a resolute Hazel, also dressed in mourning.
Hazel insists that she knows Orin killed himself and his blood is somehow on Lavinia's hands. Whatever the case, she has come to discuss Peter. Lavinia cannot marry him. The Mannon secrets will come between them and prevent their unhappiness. Moreover, she has caused strife within their family. When his mother approached him about his marriage, he left home and vowed to never speak to her to Hazel again. Lavinia commands her to leave her alone or else die by Orin's pistol. Hazel moves to go. She asks that Lavinia let Peter read what was in Orin's envelope, since she has told Peter of it already. Closing her eyes, Lavinia wonders why the dead cannot die.
Peter arrives, and Lavinia immediately tries to appear cheerful. She keeps her eyes closed in fear. They pledge their love anew. Lavinia is startled, however, by the bitterness in his voice. She makes him promise that he does not suspect her and suggests that they marry immediately. Peter suspiciously refuses, sating that they cannot marry on the day of Orin's funeral.
Lavinia flings herself into his arms, begging for a moment of joy, imploring Peter to want her. In the throes of her passion, she cries: "Take me, Adam!" Horrified Lavinia realizes that the dead will always intervene between them. She orders Peter to go home, feigning that she was indeed that native man's "fancy woman." Peter recoils in repulsion.
As Lavinia, square-shouldered, watches Peter go, Seth returns singing "Shenandoah" under his breath. Lavinia cackles that she is bound to the Mannon dead. Since there is no one left to punish her, she must punish herself. She will nail the shutters and live in the house with the dead until the curse is paid out. She orders Seth to close the shutters and have the maid dispose of the flowers. Lavinia ascends the portico and stares into the sunlight. Seth leans out of and closes the right window, and she marches woodenly into the house, closing the door behind her.
In Mourning Becomes Electra you write: "Oedipus was the Theban king who unwittingly killed his father and MURDERED his mother." [Emphasis mine].
It should read: "Oedipus...MARRIED his mother!"
(Oedipus' mother Jocasta did commit suicide after learning her lover was her son. Oedipus however did NOT "murder" her.)