Like I've said before, I understand Jennifer not telling Paige because for one, she may not have believed it (after all, it sounds ridiculous to hear that your mother slept with your boyfriend that she hates), and Jennifer didn't want to sell out her son. But the mistake Jennifer made was encouraging JJ to reunite with Paige and lie to her about everything. She should've either made JJ tell Paige the truth, or just encouraged him to move on.