Her oldest daughter Louise of the Netherlands was the mother of Louisa Bernadotte, wife of Frederik VIII of Denmark. So it may have been a loan from one of Louisa Bernadottes descendants.
Louise of Prussia was the original owner of the Pearl tiara in the Danish collection.
It is hard to determine from a black and white photo what the stones could be.
They could also be aquamarines, light yellow or white topazes, zirconias etc
Somehow I doubt that the Danish branch of the Bourbon-Parma or the Holstein-Ledreborg family would own a band of big diamonds like that.
484