...the issue with this though would be, that none of Caro's children are royal. Charlotte could have already worn a tiara but she hasn't. Either she's not allowed by court rule (Albert), or she doesn't care for it.
I don't think Charlotte is much of a jewelry person, period. She's photographed extensively and the pieces she wears are always very minimal. In any case, although she's mega-rich, Charlotte's life isn't likely to include many (or any) tiara events, unless she herself marries a royal, which is highly
unlikely. Alexandra, OTOH, is an HRH (albeit a very minor one) and will probably have an occasional tiara event when she's older.
I read somewhere after Stefano died Caroline sold some of Graces jewelry to cover his debts.
I personally would be surprised if Rainier allowed that