As indicated by the caption, this is an image of Katherine Mackay (Katherine Alexandra Duer (US1797spouse1)) taken circa 1902 with her first child Katherine Duer "Kay" Mackay (US1797a).
The caption accompanying this photograph reads:
Circa 1902: Katherine Mackay and her first child, her daughter katherine, called Kay, note the ermine robe.
See Harbor Hill, Clarence Hungerford Mackay's Mansion.