Is it certain that Caroline owns those jewels personally? From all I read about it, it was more or less what people assumed, stince she was the only one who wore the fringe tiara (as a necklace) and the pearl tiara. I can well imagine that those jewels went to the prince and Caroline wore while acting as Monaco's first lady. And if I am not mistaken, Grace had a couple of tiaras which were never worn after her death, like the Bains de Mer ruby tiara, the Van Cleef diamond tiara or the diamond necklace/tiara with the arcs. I have seen pictures of Grace with a couple of other tiaras, but don't now if they were borrowed.
It would certainly nice if they re-stard the tradition of the first lady wearing a tiara on the eve of national day. But I have the feeling they might not. We have to wait and see.