"Leading the list of attendants was Princess Maud of Fife, only daughter of Mary’s aunt, Princess Louise, the Princess Royal."
The article is wrong here. Maud had an older sister, Princess Alexandra. Interestingly, when Edward VII made Louise Princess Royal, he granted the title of Princess and the style Highness to her daughters, who would otherwise not be entitled to that as female line descendants. When George V issued Letters Patent in 1917 limiting royal titles and styles, he did not de-princess them, but asked Maud not to use her royal title. Alexandra had married Prince Arthur of Connaught previously so she was HRH Princess Arthur by marriage and Duchess of Fife in her own right (from her father).