Hi Tara:
While it would be a dream come true for me to stay for a night at Cinderella's Castle, as of now, the suite in Cinderella's Castle at Magic Kingdom is not available for booking by Guests. I imagine certain A-list celebrities may have a shot of booking the castle, but for the rest of us, the suite is not a current option.
From time-to-time, an overnight stay at the Castle may be offered for charity purposes or certain promotions. However, there is nothing I can tell you to do to be selected for any of these promotions, to the extent they are offered.
You may want to consider a stay at the
Grand Floridian Resort and Spa, considered by many to be Disney World's most magnificent, luxurious, and picturesque Resort.
Enjoy your vacation.