This name was provided by May Cooper who recalls an Aunty Agnes whom she believed to be her mother's sister. She also recalled Mary. Agnes is not mentioned on the 1881 census -so if May's recollection is correct she was born later. (Agnes was born in 1890 - she was still living with her mother in 1901.
The family account is that Sarah moved to Ashton under Lyne nr Manchester (at least her grandchildren claim they went there to visit thier maternal grandmother) - and there is a marriage record of Agnes Scally to either John Frain or Elijah B Marsland at Ashton under Lyne, 1908 Q2 8d 973. Could this be connected?
It is likely bcause from 1911 census: Agnes Frain, 21 born Hanley Staffs was with her husband John Frain, 29 a coal miner born in Hanley, Staffordshire visiting the family of Reuben and Ada Wilkinson at Seaham Harbour, county Durham. They had been married for three years and had two children, Mary Agnes 2 and May 8 months old. Both children had been born in Ashton Under Lyne, Lancashire.
An Agnes Frain died in Ashton Under Lyne in 1937, aged 47. Ashton, 1937 Q2 8d 764