From the Brookline, Mass., city directories, it would seem that Fanny was a widow already by the time of the 1879 directory. The 1910 census indicates she immigrated in 1860. The 1870 US Census shows another Kilnan family in Brookline -- Michael (aged 40), Mary (aged 45), and Michael (aged 9). It is likely they are related to your group. There is also the family of James Kilnan, aged 36, living with his mother, Ellen, aged 81, and his children.
1870 US Census
Kilnan, John, aged 42, laborer, born Ireland
Kilnan, Fanny, aged 35, keeps house, born Ireland
Kilnan, Minnie, aged 12, born Mass.
Kilnan, Ellen, aged 9, born Mass.
Kilnan, Margaret, aged 7, born Mass.
Kilnan, Elizabeth, aged 2, born Mass.
Kilnan, Norah, aged 1, born Mass.
Kilnan, Daniel, aged 9, born Mass.
The 1880 census has Fanny Killan, aged 50, a widow, living in Brookline with two daughters, Lizzy, aged 13, and Norah, aged 11, both born in the US.