By being born on American soil, it does make Lili’s birth unique.
Her uncle, Prince William, also has a unique birth story.
According to theBBC, Prince William was actually the first future king to have been born in a hospital.

Before the Duke of Cambridge, royal babies were delivered at home.
The new tradition has moved to the hospital more specifically, the Lindo Wing of St Mary’s Hospital.
That is where both William andHarrywere born as well as the Duke and Duchess of Cambridge’s children.

The couple’s son was born at Portland Hospital, a private hospital in Westminster (viaGrazia Daily).