As you probably already know, Nancy was living with her parents William and Adeline in Tangipahoa Parish in 1900. She has two sons, Augustus, age 1 and Darrell, age 4 mos. (He must have died young).By 1910 Nancy is a widow.
I found this man in 1900 - I think he is a good bet to be Nancy's husband:
1900 Union Co., Iowa census: Grable, W.M., age 31, b. IA May 1869, married 3 years, parents born MO, occupation Railroad laborer.He is a boarder in the household of Edward Perry. No wife or children with him.
It's possible W.M. was killed in some kind of R.R. accident between 1905 when Benjamin was born, and the 1910 census.