Dear Baxter, i do not think that Sybil Cholmondley is wearing sunglasses, i think that they are Tortoise shell rimmed glasses,known as horn rimmed, very popular at the time.If you look at the back row in Octavius photo, you will see a Countess with a large coloured stone Tiara, wearing similar horn rimmed glasses as well, so personally i think its just a trick of the light on her lenses? Regards CMM