FamilySearch shows her maiden name as "Bubb," but the marriage record of her marrying a John Roberts shows her maiden name as "Babb." Indications are that she may have married another man by the name of John Roberts, rather than the man who is in the 1856 James G. Willie Company.
She sailed to America in 1856 on the ship Thornton. Mary Roberts and a John Roberts were on the same ship, but the ship manifest lists them on separate pages, not traveling together as a family.
Further research is needed to confirm who her husband was.