At the time of the Regan Administration numerous press items reported that a considerable amount of the jewels worn by Nancy Regan were lent to her by her wealthy friends. But some of the jewels were her own.
Here is a link to the Christie's 2016 sale of some of her belongings. The jewels are scattered throughout the catalogue.
https://www.christies.com/features/A-First-Ladys-jewels-and-handbags-7613-1.aspx Nancy Regan wearing jewels, which I suspect were lent to her.
Some of the pearls which Nancy Regan was photographed wearing may have been her own as there are several strands in the auction catalogue.
The necklace and earrings seen in the photo below belonged to her. They are in the auction catalogue.