In the follwoing article you can find a few statements that have been released by the Imperial Household Agency:
** the-japan-news.com: Crown Princess Masako celebrates 51st birthday
And here are the official birthday pics, as usual taken a bit earlier. On pic 2 they are looking at a book that was presented to them by King Willem-Alexander and Queen Máxima during their latest visit.
On her birthday, December 9, Crown Princess Masako visited Emperor Akihito and Empress Michiko at the Imperial Palace (pics 4&5).
** Pic 1
** Pic 2
** Pic 3
** Pic 4
** Pic 5