Thank you everyone for the contributions.
Over night my subconscious was endeavouring to deal with what I think is a discrepancy between the shape of the pearl Empress Eugenie was photographed wearing and La Regente.
Despite the impression I have that the pearl is very large, I wonder if the shape fits with that of La Regente?
I have tried to visualise what the pearl would look like if it rolled, and yet I am still left with queries. Basically I cannot see that La Regente, even if the pearl had rolled when the photo was taken, could match.
Some side views of La Regente which might help others to decide.
This detail is from http://diamantsdelacouronne.free.fr/Diamants%20de%20la%20Couronne/Parure%20de%20perles%20et%20diamants/slides/Parure%20de%20Perles%20-%20Regente%203.html
I also doubt if the surmount to the pearl worn by Empress Eugenie matches that of La Regente as it was set during her era.
Eventually I began to wonder if the Empress might have been wearing the element in the second section of the corsage brooch.
Side by side comparisons.
(1) The Empress, (2) the second section of the brooch, (3) La Regente.
What do others think?