An enamel and diamond brooch

An enamel and diamond brooch, possibly Switzerland, late 19th century, designed as a circular plaque finely painted in enamel to depict a woman with white hair wearing a crown, against a pale blue basse taille enamel ground, accented with rose-cut diamonds, within a floral frame topped by a pair of birds, set with rose-cut diamonds and circular-cut rubies, length 3.4cm, unmarked