I thought I might give this a go. I'm not a big fan of existing royal aquamarine tiaras but I thought the tiara the Countess of Wessex wore looked pretty good. I also added in the chandelier earrings to round off the parure.
I also though that Mary's wedding tiara in pearl setting, her pearl choker, and wedding earrings (with other pearl jewels) would make a lovely pearl parure.