Two of the most important choices Elizabeth makes that affect the outcome of her story in this play happen before the play even begins, although both are referenced several times by characters: the choice to confront her husband about his infidelity and her decision to dismiss Abigail Williams from the Proctors' service. She and John discuss both of these choices in Act Two.
In Act Three, Elizabeth makes the choice to lie to the court about her husband's infidelity. She is attempting to save John's reputation, and assumes he did not tell the court the truth about his sexual relationship with Abigail, so even though she never tells lies, she lies this one time. This ends up confirming, in the court's eyes, that Abigail is telling the truth, not John. If Elizabeth had told the truth, she would have freed both herself and her husband, and perhaps have ended the trials altogether. Elizabeth's choice to lie indirectly leads to John's arrest and eventual death, as well as her own widowhood.