You need to tell your cousin to withdraw her application and that if she does, you'll keep your mouth shut about her fraud. She put you in a very bad situation because you have an obligation to report known fraud. It's worse when it's the same employer. If she was doing this to the place down the street, who knows?
If she doesn't withdraw her application, you'll need to report her. Yes, blood is thicker than water but dragging an unwilling family member into a crime shows how little she thinks of family bonds.