The tiara worn by Sarah, Duchess of York following her marriage [she walked up the aisle wearing flowers, with the tiara actually 'hidden' below her veil, to be quickly subsituted for the flowers whilst she was signing the register] has an interesting story.
The Ferguson family did not have their own family tiara, and so the one which Sarah wore at her wedding had initially been hired by her family from Garrard, who were then the Crown Jewellers. [hiring tiaras is not unknown in the UK even among titled families, because death duties etc have often meant that family tiaras have had to be 'sacrificed' to pay the bills etc]. It was then that the queen decided to buy the tiara for Sarah. Many Royal watchers took that to be a common sense decision (as well as a generous one) on the part of Her Majesty - had she not bought the tiara for Sarah, it would have been returned to Garrard, with the chance that in due course they would have hired it out to another person. One occasion when tiaras are worn is during the State Opening of Parliament - imagine the fun that certain sections of the British Press would have had saying 'Oh, look at Lady XYZ in all her borrowed finery - she is wearing the tiara that the Duchess of York wore a few months ago at her wedding'.
Whilst this observation probably belongs more properly on another thread, Sarah Feguson actually 'did quite well' with the jewels she was given. Many presents made to The Princess of Wales by the queen were in fact 'Royal' jewels, which would always be understood to revert to the Queen / The Crown after her death [which indeed was the case]. Even when her marriage was strong, The Duchess of York received no such 'Royal Jewels' if you see what I mean. The Queen very generously made lots of presents of jewellery to Sarah, which she retains. No doubt people here remember the jewels that were stolen from Sarah's luggage at New York airport - they were all 'personal gifts' she had received.
Alex