Genevieve,
Tell her to do absolutely nothing. That feature is fully automatic.
The email your friend received with her username/password right after buying the PrepCast Elite included the following information:
"Additionally, your 90-day access to The PM Exam Simulator does not start immediately. Instead, the simulator "waits" for you to log in and start your first exam/quiz. Now the simulator asks, "Do you want to activate your account?" If you answer "Yes, activate", then your 90-day access begins and the expiration date is set to the correct date. Please note that simulator activation is irrevocable. It cannot be reversed."
So as long as she doesn't start an exam or quiz in the simulator the 90 days do not start. But once she starts the first exam or quiz then the clock starts ticking.