Its interesting that Queen Louise was a Swedish princess and she received many Swedish items which on any logical thought process should have been kept within the Swedish collection - I am thinking not only of the Pearl parure but also the Diamond tiara and Emerald parure now worn by Queen Sonja. I believe there is a pink Topaz parure of Queen Louise's originally from Sweden which was inherited by her eldest daughter and then passed into the extended Hohenzollern family and is now held by the Albion collection in Japan.
The current Bernadotte jewels are arguably the joint second best collection in Europe (along with the Dutch) but imagine if all of the jewels of the first three Bernadotte Queens had been placed in the Bernadotte foundation? It would arguably be the widest and finest collection bar none. Thanks to Queen Louise the Pearl poire tiara has been preserved for Denmark but it is through pure luck of course that the Diamond tiara and Emerald parure worn by Queen Sonja found themselves into the Norwegian line. Different life choices could have resulted in them ending up like the Pink topaz parure.
The idea that the Pearl necklace coming from a foreign ruler was the reason for its selection for the trust is an interesting one. Absent some contemporaneous evidence its difficult to consider. I recall reading that Queen Margrethe herself couldn't quite explain why her ancestress received such an extraordinary gift from the ruler of a distant land with no blood relation.
Its interesting that two of the most beautiful pieces of jewellery that have passed through the Danish royal house in the last two centuries came from the Khedive of Egypt - Queen Louise's necklace and Crown Princess Margaretha's Cartier tiara. In terms of the latter, one may speculate why the Swedes did not think a wedding gift from a foreign ruler to their Crown Princess was of sufficient importance that it needed to be kept from future Swedish royals and was instead allocated to her daughter, who fortunately became Queen of Denmark and meant it was retained by a royal house at least for the 20th century. No disrespect to Queen Ingrid or Queen Anne Marie but I thought it was a great shame that it was bequeathed to Queen Anne Marie simply because now that Greece is a republic over the generations that follow it will likely be sold or disappear from view for decades at a time. Would have been nicer had Queen Ingrid left it to the Danish Royal Property Trust.
Questions beget more questions and mysteries!