Ava was already screwed up at that time. She had trusted Elijah so much that she just failed to notice his real intentions at that time. He once told her that his wife is not talking with him nicely now a days and even went to visit someone every day behind his back. When he asked her that where she is going, she just simply said that she is going to her friend's house, but the reality is something else.
That's why he asked Ava for his help and also told her to act like his girlfriend and it will be remain secret in between them and once her wife will get jealous and will confess him the truth then their deal will be done at that time and no one will ever tell their top secret to others. And Ava just got immediately agreed with his plan because that was the exact opportunity she was looking for only to see that, does Ace gets affect by it or not? So they both made a perfect plan to make jealous his wife and Ace.
