There is no restriction on X Plan sales requiring them to be ordered units. Dealers sell vehicles out of stock as X Plan sales all the time and get their X Plan commissions from Ford. Her Dealer just doesn't want to deal with it figuring they'll hold out for an even higher profit retail sale.
Exactly (guess I didn't state that clearly). X plan is optional and the local dealers, including my dealer, decided not to accept it for Navigators at the moment as they believe can get more for the vehicle due to demand. My dealer is willing to sell me one at x-plan, however, if it is custom ordered, which is what I did for my sister.