The 1870 federal census was the first time that "Indian" was added as a choice under the question of race. You could try reading the census records for the area to see if there are any indications of other Indian families. Have you found Olive in 1870? Is she listed as "Indian"? Note: As a former genealogist for the Bureau of Indian Affairs I can tell that there are many, many family stories of an Indian ancestor that can never be proven.