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:
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:
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.
It does not take long after Elizabeth's introduction to fully understand that Abigail's motivation is to separate her from her husband. Once Mary Warren discloses that Elizabeth was a target of the accusations, Abigail seems to recognize immediately a couple of truths that will be present throughout the drama. The first is that Abigail is "calling the shots." Anything and everything Abigail is saying is "being taken as gospel." Elizabeth fully recognizes Abigail's power in this Act. Accordingly, Elizabeth also understands Abigail's true motivation has to do with vengeance for being dismissed and coveting John Proctor. Witchcraft is not the primary motivation. Rather, it is the desire to advance her own agenda. Elizabeth clearly grasps these elements. It is also at this point that Elizabeth recognizes Abigail's danger, making standing up to her both an absolute necessity and one that is extremely dangerous.
Elizabeth understands that Abigail’s motivation is to get rid of Elizabeth so that she can have John all to herself. It becomes evident fairly quick that Abigail will go to any extreme necessary in her pursuit of John. From accusing others, to planting the needle, or at least seizing the opportunity of it being placed in the doll’s stomach for “safekeeping,” Abigail is relentless in her pursuit to bring down Elizabeth Proctor. Elizabeth understands Abigail’s motivation because John told her of the affair, and with the accusations flying, even before she is accused, Elizabeth understands that her time will come once she is told by Mary Warren that her name was mentioned in the court. Plain and simple, Abigail’s motivation is a pure obsession to be with John at any cost, and her assertion that Abigail is “murder” and that she must be “ripped out of the world” indicate that she is fully aware of the severity of the danger that Abigail is about to bring on their lives.