Mary, upon marriage, acquired the use of the
Désirée diamond and ruby parure which remains one of Europe's finest. The parure was bequeathed to Frederik as was the expressed wish of the late
Queen Mother Ingrid.
Mary is also the only European
Crown Princess with a parure reserved for her sole use.
The Crown Princess's wedding tiara is her personal property. It was a wedding gift from the Queen and Prince Consort and as such, belongs to her personally. Should Mary and Frederik divorce
(and we certainly hope that never happens), then Mary would henceforth relinquish all use of the parure and Crown property
(if she were Queen at the time), and be left only with the personal items she has either bought or received. Being the mother of a future King, it is entirely appropriate that Mary should establish her own jewellery collection beyond that of the state's.
It's understandable,
imo, that the wedding tiara is smaller as Mary has the use of the ruby parure and stands to inherit the exclusive use of foundation and crown jewellery in years to come.
Princess Marie's tiara is a loan and thus, is still owned by the Queen but is worn by Marie with regnal consent.
As for Alexandra's tiara, the Queen evidently learnt from this misguided judgement which would explain why Marie was not gifted a tiara from the royal collection
(as was the case with Alexandra) but instead is allowed the permanent use of one. This arrangement was confirmed by the court and ensures that the tiara does not leave the royal family.