According to the 1900 census, George immigrated in 1879, so there's a good chance Sarah came with him at that time.
1880 U S Census: Passaic, NJ
Roberts, George
Sarah
Harriette E, b. Nov 1879, NJ
1885 Census Passaic, NJ
George Roberts, foreign born, age 20-60
Sarah A Roberts, foreign born, age 20-60
Harriett E Roberts, age 5-10
George G Roberts, age 0-5
James A Roberts, age 0-5
1900 U S Census: Passaic, NJ
Roberts, George, b. Apr 1847, age 53, married 5 yrs, b. ENG, ENG, ENG, immigrated 1879, Nat.
Mary, b. May 1868, 32, married 5 yrs, mother of 3 children, 2 children living, b. IRE, IRE,
IRE
George, b. Apr 1881
James, b. Aug 1884
Alice, b. May 1887
Sarah, b. Mar 1896
Cooper, Veronica, step dau, b. Mar 1889
1905 Passaic, NY census
George is a widow living with the the 4 children, excludes George Jr.