Yes, she can terminate you if you don't sign the agreement, unless you already have a still-in-effect (i.e. not expired) written employment contract protecting you from termination in a situation like this. Otherwise, in the absence of an enforceable written employment agreement, all employment is "employment at will" and your employer can change the terms or conditions of employment at any time (i.e. at will), such as by requiring employee's to sign an infraction agreement if they want to keep working there, and terminate anyone who does not accept those terms or conditions.