Here is the segment of her email where it's described:
" If you want to purchase the Apple Watch in store, you will need to make a reservation. Beginning April 10th, you can make a reservation to purchase a specific Apple Watch model in-store as early as April 24th. Your reservation will be for a specific time, much like if you were coming in for a Genius Bar appointment. You will pay for your new watch at that time. Having reservations for specific times will allow you to purchase the Apple Watch without waiting in line, and allow the Specialist who assists with your reservation to provide you with the best experience possible."