If what has been written by Field is correct then the Queen would have been in possession of the so called Indian pearls by 1855 when Winterhalter painted the portrait.
They are said to have been part of the Treasury of the Punjab which was annexed in 1849.
The East India Company then presented the pearls, along with the Koh-i-noor, to Queen Victoria, who allowed the diamond to be displayed in the Great Exhibition in 1851.