Thank you, Vincent, for these explanations, and sorry for having brought an erroneous information.
I remembered that the current Count of Paris had declared in Point de vue in February 2012 that the sapphire earrings worn by his daughter-in-law Philomena at Princess Antoinette's christening were indeed the Crown's sapphire earrings, and that they had been presented as a wedding gift by King Simeon II of Bulgaria to Marie-Thérèse of Wurttemberg when the latter had married the current Count of Paris (then Count of Clermont). But as we had absolutely no picture of Marie-Thérèse wearing these earrings, while we had, on the contrary, pictures of Isabelle, Countess of Paris, wearing them, I had supposed that the current Count of Paris had made a confusion between a wedding gift to his mother or to his (first) wife - and the confusion seemed to me even more plausible since the current Count of Paris is quite estranged from his ex-wife Marie-Thérèse. And if the idea of a woman using jewels of her mother-in-law seems quite natural, the contrary (a woman using jewels of her daughter-in-law) seemed weirder to my mind...
But considering that you had the best sources of information about these earrins, I now fully trust you.
I just bring one small correction to what you wrote: Isabelle, Countess of Paris, did not wear the Crown's sapphire earrings "once", but at least twice, as shown on these pictures from two different (unidentified) occasions: