Hi, Amanda!
Great question! (And great restaurant selection, too!)
When you make your Advanced Dining Reservation for
Cinderella's Royal Table simply make your reservation for two people. You won't be seated with another party, so that part is simple. Either make your reservation online at the link above or call Disney Dining at (407) WDW-DINE.
While the location of that table for two is a bit more complicated, you could certainly make the request. Either call Disney Dining at the above number or, at the very least, tell the Cast Member when you check in at the restaurant your request for a seat by the window. That Cast Member can't make any promises, but it will good for him or her to know of your preference should a table by the window become available at the time of your seating. (If there is any special occasion that you are celebrating, be sure to let the Cast Member assisting you know that, too!) It could help if you get to CRT early, letting the CMs at the restaurant know about your request as soon as possible as well. That, combined with an early arrival, will make it easier to fulfill your request if it is at all possible.
Have a wonderful time, Amanda! Send more questions as you think of them; we love to help!