Interesting.... but the wedding is also a symbolic gesture of granting sovereignty and therefore, a tiara is most expected regardless of her common status, which at the point they say "I will" defines the transition point.
Regarding tiaras for Kate; Princess Diana nor Sarah donned one of the Queen's tiaras for their weddings. My opinion is that HM will have one made for Kate as she did for the Duchess of York.
I'm a newcomer and still fumbling around with the tabs, pages, etc. so I'm feeling totally inadequate at this point. I'm not overtly informed about royal musings nor am I overtly formal. Just enjoying the different interests, etc...
Susan
I hope it's The Girls of Great Britain & Ireland Tiara
But given the fact this was a wedding present to HM by Queen Mary, it is doubtful. IBut I think it is a significant tiara to add to the majestic aura of the occasion and to Kate's statuesque beauty.