What does Elizabeth understand about Abigail's motivation in The Crucible?

If we examine Act 2 carefully and in particular the
suspicions that Elizabeth has about her husband and Abigail, and then the news from Mary
Warren concerning the trials, it becomes clear that Elizabeth believes that Abigail is
manipulating the situation so that she can get what she wants: John Proctor, having
disposed of her. Note what she says after Mary Warren has told her that she has been
accused: "Oh, the noose, the noose is up!" Having said this quietly, and then hearing
her husband deny it, she responds with:

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She wants me dead. I knew all week it would come
to this!

Trying to explain to
her husband how this could be possible, Elizabeth tries to explain to him how his
understanding of young girls is "faulty," and that sleeping with a young girl is
actually tantamount to giving her a promise:

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Spoke or silent, a promise is surely made. And
she may dote on it now--I am sure she does--and thinks to kill me, then to take my
place.

From what we have seen
of John and Abigail's first encounter in the play, he has done nothing really to
discourage her. Interestingly, his wife's words are accepted by John Proctor later on in
the play when he reveals his sin of lechery and accuses Abigail of wanting to dispose of
his wife and then marry him.