Elizabeth, being at home working all day while John is in the fields, is privy to more gossip and information from the town.  People pass by her house and share the news, and she has had time to process it while John has been working.  To start off with, she has heard that Abby

"brings the other girls into the court, and where she walks the crowd will part like the sea for Israel.  And folks are brought before them, and if they scream and howl and fall to the floor-the person's clapped in the jail for bewitchin' them."

So, she has heard just how powerful Abby has become-anyone brought into the courts is automatically charged with witchcraft simply through the actions of Abigail.  So, when Elizabeth is charged, she knows that Abby has pointed the finger at her, and Abby is powerful in the town now.  She knows from that that she doesn't have much of a chance.

In addition to this, Elizabeth, being a woman, probably understands more clearly a woman's vengeance.  She knows just how deeply Abby wants her husband; she felt her wrath when she fired her, and she understands that a young girl, courted by a man like John Proctor, falls for it and thinks he has given her promises.  She says to John,

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

She understands that Abigail wants John still, and that Elizabeth is the main obstacle in the way of that.  John can't quite see that perspective yet; he still has a bit of a softness for Abby. He has only seen the good in her, and so doesn't believe Abby quite capable of such evil.  His perspective is skewed by their affair still, and the fact that, being a man, he doesn't understand how jealous women can get.  Elizabeth understands perfectly that "there be monstrous profit" for Abby in her getting arrested.  She tries to tell John, but he will have to learn first-hand just how far Abby will go.