In the 4 death records of her children included here, one calls her Bettie Thomas and the other 3 give her maiden name as Green. Since she had a son with a middle name of Green, taken together with the death records, it seems more likely that her maiden name was Green than Thomas.
1910 U.S. Census Population Schedule Name: Betsey Steele [Belsey Steels] Age in 1910: 98 Birth Year: abt 1812 Birthplace: Tennessee Home in 1910: Civil District 1, Wilson, Tennessee Race: White Gender: Female Relation to Head of House: Mother Marital Status: Widowed Father's Birthplace: Virginia Mother's Birthplace: Virginia Household Members: Name Age Robert L Steels 37 [Betsey's youngest son Robert Lee Steele] Elvira Steele 36 Bedford Steele 17 Effie Steele 7 Makus Steele 4 Betsey Steele 98