Margaret's death certificate shows her name as "Margaret Oakley Best," and the Utah State History Cemeteries and Burials Database shows her name as "Margaret O. Best."  

FamilySearch has her name as "Margaret De Groot Best," but there is no primary source showing a middle name of "De Groot."  A history of Margaret written by her daughter Caroline, which appears in FamilySearch, shows her mother's name as "Margaret Oakley Best."  Margaret would have given her name at the time she received her patriarchal blessing, and the Early Church Information File shows that she gave her name as "Margaret Oakley."  The Wells Ward, Record of Members does not include a middle name.