I think your suggestions could be correct Hollie. The Empress had an eye for jewels and it could have been a gift or very well used as collateral. The replacing of some of the stones with paste substitutes is intriguing. It provides an answer why this piece has never been worn in public by any Royal woman.
Of course, no one would wear the cameo because of the ivory used and it may be that the entire piece is in fragile condition now.