Obsession over continence is nothing new in Royalty. The French Monarchy for example were obsessed with enemas where is was considered the highest point of fashion and the French nobility did not have to concern themselves for where they went potty. It was not uncommon to see Maids diving under dresses to apply an enema and allowing the Lady to relieve herself on the spot. Meanwhile the Maids themselves had to endure a strict potty schedule, each receiving an enema before they started work and control their bowels.
It would not be hard to take a leap into a fantasy of a padded monarchy when close enough things have already happened in reality. Could very well become fashionable to see the high born strut around in diapers with the servants cleaning up after them.
With Grace though it is a question of how she would look to rule? With diapers and spankings for the unruly subjects or to horde that as a sign of luxury for herself? Will she rule as a tyrant with her subjects over her knee with their backsides whacked till they wet their padding? Or will she prefer to be a hedonist that lounges around enjoy leisure activities while a servant wipes her bottom clean?