Perhaps Margaret's mother is Polly Dunn, since she is living with James and Margaret in 1860.
Husband remarries in 1872, so she is probably deceased.
Noted events in her life were:
1. Census, 1850, Montgomery County, North Carolina, United States. Margaret Green is 28, living with husband James M Green. (Montgomery Co, p115)
2. Census, 1860, Montgomery County, North Carolina, United States. Margaret Green is 39, living with husband Jas M Green. Also there is Polly Dunn (57, property 35). (Montgomery Co, Mt Gilead District, Mt Gilead PO, p1032, family 1035)
Margaret married James M. GREEN, son of Anderson GREEN and Sarah STONE. (James M. GREEN was born in 1821 in Montgomery County, North Carolina, United States.)