Do you know the date of her marriage please?
Yes, there was a 1915 census in NY. And one in 1921 (Canada). The couple are in the 1921 census, as well.
New York, New York, U.S., Extracted Marriage Index, 1866-1937Name: Esther Greenland
Marriage Date: 15 Jul 1916
Marriage Place: Manhattan, New York, USA
Spouse: Susman Hershorn
Certificate Number: 17050
Name Susman Hershorn
Age 27
Birth Year (Estimated) 1889
Birthplace Radno, Russia
Marital Status Single
Father's Name Wolf
Mother's Name Mary Woodruff
Spouse's Name Esther Greenland
Spouse's Age 19
Spouse's Birth Year (Estimated) 1897
Spouse's Birthplace London, England
Spouse's Marital Status Single
Spouse's Father's Name Jude
Spouse's Mother's Name Anna Fligel
Marriage Date 15 Jul 1916
Marriage Place Manhattan, New York, New York, United States