Mildred Cecilia Harriet Sturt (1869–1942) married Henry Arthur Cadogan, Viscount Chelsea in 1892 and had a son and five daughters, all of whom married titled men. Mildred's sister-in-law, through her brother Humphrey, was Féodorovna, Lady Alington. Henry died of cancer aged 40 in 1908 and two years later Mildred married Admiral Sir Hedworth Meux, pronounced 'Mews'. He had changed his named from Lambton in order to benefit from the will of Valerie Susan, Lady Meux. She left him a lot of money that she had inherited from her husband. She was American.
The twirls in the middle are the letters MC.
Bookplate (click to enlarge)