In my opinion, the choice of mantilla versus hat at a Catholic church service is entirely a matter of personal choice. Neither is more ``Catholic'' than the other. And as far as the ``privilege blanc'' is concerned, that is only in the context of meeting with the pope.
I would assume that most of the royals who were in attendance there have a ready set of mourning clothing to be worn. I know that Queen Elizabeth always traveled with a set just in case, and, alas, in came in all too handy when she and Philip were in Africa and her father died.
The type of Catholicism that Katie subscribes to does require a chapel veil to be worn to mass. They are subscribing to an outdated and overturned (by Vatican II) form of Catholicism that was pretty much the norm before 1962. Yes, it's a personal choice in YOUR view; in Katie's, it is not.
Actually while Vatican II did allow the mass in the vernacular, the extraordinary form was never overturned. You can go to a latin mass today, which is totally legit. Also, while I don't know Katie's views, not all people who go to or prefer the extraordinary form are the crazies who believe that there hasn't been a legit pope in however many years. Those SSPXers are cray.
That would be the Mel Gibson splinter 'catholics'?