How does the author use foreshadowing in A Delicate Balance: A Play?

At the end of Act I, Claire, Agnes's alcoholic sister, enters and apologizes for her somewhat inebriated condition. She then accuses her sister of mistreating her because she is a drunk. Agnes defends herself in a way that Albee's heroine has never done, foreshadowing the change that will take place in her by the time the play ends:

AGNES: . . . If I scold, it is because I wish I needn't. If I am sharp, it is because I am neither less nor more than human . . .