Cristina, you don't have an archive: you have a gold-mine. I do not know what to think about this bow brooch:
1. Sure that D.Isabel family is a noble one but the Royal vaults probably have much more jewels than her family vaults. Why would the Duchess wear a Heredia jewel with so many Braganza jewels to explore in 1998 (only 3 years of marriage)? May that brooch be an Heredia heirloom with special meaning?
2. May this brooch be a wedding present (so, personally owned by D.Isabel) that the Duchess loaned to her mother?
3. May this be a Braganza heirloom that was loaned to D.Raquel? It seems similar to the brooch used by D.Maria Adelaide in her 100th birthday. If so, it is owned by the Duke, not the Duchess, so he would have to agree on the loan.
Whatever the option is true I hope the brooch becomes part of the main line of the Royal Family because it is a beautiful piece.