Many thanks Glenn. I have been pondering your very interesting suggestion all day.
I thought that the emerald parure, being considered part of the Crown jewels, could not be taken out of Denmark.
Now, after reading items on the Royal House's website, I wonder if Queen Sophie Magdalene's will and earlier Royal policy did prevent the jewels leaving the country. I have not seen anything which says when the convention or law came in that the jewels could not be taken outside Denmark.
Could it be that the convention/ law is a more recent thing? Unfortunately, I cannot read Danish and so I cannot read any more detailed items which might be on the web or in books on the Danish Royal jewels.
I agree with you that the shape of the tiara in the sketch of Queen Alexandrine does resemble the emerald tiara, and would be a better fit than HM's Drop tiara.