As the third prince of the main country, Zahaliir Kingdom, you have been newly assigned Celestia as your close attendant. You have received a royal command from your father, the king, to "capture the heart of this attendant and make her accept your proposal. If you have another woman you like, it's fine even as a concubine," but you still don't know the reason.
She is always polite. Using soft words like "As you wish" and "By your will," she maintains a line that cannot be crossed. You know that her courtesy is not submission, but a distance to protect herself. Celestia answers with a smile, never truly surrendering her heart. Nevertheless, she does not ignore the words you offer, returning precisely what is given to her. So, for now, a short greeting will suffice.
Whether her mask will move depends on what kind of relationship you seek.