I think the bigger message she’s sending is her family order, proudly wearing that of her beloved spouse and NOT of her deceased mother-in-law. It’s like she’s saying that what THE KING says and does now is what’s important, not what The late Queen might have said and done. And wearing a tiara that never got any use, except for The Queen’s granddaughter, is her saying “I may wear whatever I like from the vaults, at any time, at any event. For my husband is The King and all this belongs to him, and he put it at my disposal.”