There is also the subject of her Coat of Arms as members of the British Royal Family are usually assigned a Label of difference in time for their 18th Birthday.
At the time of her parents' marriage in 1999, Edward and Sophie requested that their children should be known by the titles used by the children of an Earl and Countess. (Edward was granted the title of Earl of Wessex, rather than the usual dukedom, because he will eventually take over the late Prince Philip's Dukedom of Edinburgh. Earl is also his nickname, taken from the initials of his names - Edward Anthony Richard Louis.) This request was granted by The Queen via a Buckingham Palace press release. According to Letters Patent still in force from 1917, Louise is legally entitled to be called HRH Princess Louise of Wessex and retains the rank of princess, but her parents wanted her and her younger brother, James, Viscount Severn, to lead as normal a life as possible and then to choose. The use of the HRH would carry with it duties to do with the Royal Family which would have to be paid for out of the Sovereign Grant.
There was no announcement on Monday. In fact, as far as the rest of us were concerned, there was no fuss made of Lady Louise's Birthday made at all. She remains a Member of the British Royal Family, but is not, so to speak, a Member of the Royal House.
There is a precedent, although it was handled slightly differently. HRH Princess Patricia of Connaught, granddaughter of Queen Victoria, requested to relinquish her titles on marriage to naval Commander (later Admiral) Alexander Ramsay in 1919. The Royal Warrant was granted on 25th February, 2 days before the ceremony. Since the Royal Warrant stated that her change in style took effect only upon the solemnisation of her marriage, she entered Westminster Abbey as a Princess and Royal Highness and left as a Lady, the daughter of a royal duke. Lady Patricia Ramsey remained a member of the British Royal Family, remained in the line of succession, and attended all major royal events including two Coronations when she was dressed in the robes and Coronet befitting of her rank.
There has so far not been an announcement regarding Lady Louise's Coat of Arms. She is due to be assigned a Label of 5 points as the grandchild of a monarch. It is not, however, unusual for this not to coincide exactly with the Birthday in question. Whilst both Prince William's and Prince Harry's Label were officially granted on the day, Princess Beatrice's was announced a month before and Princess Eugenie's 4 months after. The Duchess of Cambridge's Coat of Arms (via her father) were announced 10 days before her marriage and The Duchess of Sussex's 6 days after hers. We will just have to wait.
It is expected that both these Princesses, being in direct line to their respective Thrones, will be appointed to their respective Council of State, although they may not yet be expected to take up active service until after their studies. They will both more than likely be granted their country's highest Order of Chivalry. Whether this is done during a ceremony such as was the case for HRH Princess Elisabeth of Belgium, Duchess of Brabant and HRH Princess Leonor of Spain, Princess of Asturias, we will again have to wait and see...