According to the 1871 Census, Maria Shank (née Miles) was aged 27 and born in Pulham Norfolk.
I can see only one candidate for her in the 1861 Census.
1871 Pulham St Mary Magdalen, Norfolk
Twitshall <?> Road
Francis Miles, head, 65, ag labourer, Pulham Norfolk
Mary, wife, 76, Bressingam Suffolk
Maria, grand daur, un, 17, glovemaker (leather), Pulham Norfolk
Emma, grand daur, 4, Pulham Norfolk
Clearly she was very young when Walter was born in 1859.
1851 Census: She was with her grandparents Francis and Mary in Pulham. The other members of the household included her unmarried mother Mary Miles.
So we have two challenges:
Who was the father of Maria Miles?
Who was the father of her illegitimate son, Walter?