The Bureau of the Royal Household announced today (Wednesday) that members of the public can write their get well and good wish messages in books for HRH Princess Bajrakitiyabha Narendira Debyavati at King Chulalongkorn Memorial Hospital until January 31st.
After that, they can still express their wishes to the Princess every day via: https://wellwishes.royaloffice.th
Books for the public to express their good wishes have been available since the Princess was admitted to hospital on December 15th.
Source: Thai Public Broadcasting Service