Identified as 'M.C.G. Lysley' in the Silvy daybooks, the likliest match I can find is the wife of barrister Warine Bagley Marshall Lysley, who appears on the 1861 census living with his young family at 38, Queen's Gardens, Paddington, a mere stone's throw from Silvy's studio. His wife's forenames, however, were Lavinia Sophia, so either there's a mistake in the daybooks or I haven't found the right woman.