A lovely coverage Cristina. The fern is a new Zealand emblem and was worn in New Zealand. I would just point out that "heirloom" is used in the expression "heirloom of the crown" which refers to specific pieces that have been identified as such, eg, the Oriental tiara. We are not likely to see the Duchess of Cambridge wearing any heirlooms of the crown until she is Queen.
Perhaps family jewels (or royal family jewels to distinguish from the Middletons) might be a more suitable expression until then? Quite a time away I would agree.