Winnaretta had more than the death of her sister to shoulder as 1896 came to an end. In addition to a grieving husband, Belle-Blanche had also left behind three young children, two boys and a girl. Soon after the funeral, Belle's widower, Élie Decazes, asked his sister-in-law if she would be willing to take charge of raising his six-year-old daughter. It was thus that Winnaretta became a surrogate mother to Marguerite “Daisy” Decazes. Winnaretta adored her niece; less clear is what kind of maternal figure she was capable of being to the little girl. Like her aunt, Daisy was the somewhat plain daughter of an extremely beautiful mother; like her aunt, she manifested her natural willfulness by lapsing into inscrutable silence. But for now, Winnaretta did what she could to act as an emotional mainstay for her niece. Daisy and her clothes and dolls were moved into the rue Cortambert house. For the next thirteen years, until her marriage in 1910, Daisy Decazes would spend a portion of every year living with her Tante Winnie, often accompanying her on her far-flung travels.

The presence of a child in the Polignac household in 1897 did not significantly affect Winnaretta's and Edmond's life. Children in the upper classes were traditionally cared for by governesses and servants. Edmond's involvement in Daisy's life was probably minimal. He was primarily concerned with assuaging his wife's grief. To lift her spirits, he bought her a special birthday present that year: an 1851 edition of the complete works of Bach.

During this period the city of Paris was experiencing the dramatic changes of modernism brought about by industrialization. More cars were to be seen in the streets among the horse-drawn carriages and bicycles. Households that could afford them installed their first telephones. For the music- lovers who did not wish to brave the crowds at the theaters, another new and curious electronic device, the théâtrophone, allowed subscribers to hear live broadcasts of productions at the Opéra and the Comédie Française through a receiver connected directly to the various theaters.