I ve read in many posts concerning Mary's jewellery that is weird Marie's diamond tiara is bigger than Mary's but, to tell the truth, I really don't feel sorry for Mary having a smaller diamond tiara than Marie, because:
a) Marie's tiara is just a loan form the royal family ,while Mary's is at least her own personal property. Marie will only have her own tiara if QMII leaves a tiara to her or to Joachim - if not she will be on loan probabbly for ever.
b) Once Mary becomes the Queen she will have a vast collection to choose from. Marie will most likely stuck to her tiara.
c) she is the only Crown Princess who has a whole parure at her exclusive disposal. And not just any parure, but a parure which is a historic piece as well. It dates back at Napoleon's time right?
By the way, I can't understand why Mary keeps buying all these Dulong's jewel. They look very similar to me ( some even identical). She could on the other hand raise money and buy a nice classic piece with semi precious stones instead.