Another Tiara Hypothesis
The last time I ventured a tiara opinion, I learned from fellow 'forumees' that I knew very little about the rituals of tiara owning/loaning/wearing of the BRF. But I'm going to stick my neck out again.
IMHO: Judging from KM's general taste in wardrobe, I think that if (a BIG IF) the full tiara collection is opened to her, she might just choose a fringe or the kokoshnik because they have simpler lines yet are very elegant. Some of the others, including the Strathmore, are quite detailed and to me have the look of being from another age about them -- and this is in spite of the fact that I find the Strathmore to be quite lovely!
I think in particular if she chooses to wear haute couture, she may want a tiara of simpler lines. (BTW, I am a designer, and I admit my personal taste affects my opinion.)
It also seems to me that the Girls of GB could work with just about any style. It really is an amazing piece. I also think The Lover's Knot seems quite detailed and is too stylized to wear with high couture, but would look great on KM for subsequent usage. (The Diana issue should be tabled forever IMHO.) I noted that QE II wore it when she was young. With its swinging pearls and love knots, it is a fabulous young woman's tiara (despite the fact that Q Mary wore it until she was quite old). At any rate, just some thoughts to put out there.