You are very welcome. You may have some trouble finding your family on the census records, as there were multiple marriages. You should send for Sallie R Back,s death cert. Sallie R Back Death 23 Oct 1971 Lincoln, Oregon Birth: Aug 1897 Spouse: Elmer Back. Hopefully it will mention her parents names. You also might see if you can locate an Obit for Sallie.
On the 1900 census Sallie,s mother is listed as Nola. I could not find a marriage for Nola to Douglass Casey. Nola died by 1910, as Douglass is listed as a widow. Douglas Casey married a 2nd time in 1910 to a Rina / Rena Tompkins. Rena is listed as Irene on the 1920 census. Irene was first married to a Tompkins, and had several children in this marriage.
Also Sallie Rebecca (Reba) Casey was married to a Lewis W. Austin in Tulsa Co. Ok. and had several children by him, before she married Elmer Back .
If you need more help, just let me know. In order to trace Native American heritage, you have to know who your family is first. There were over 500 different tribes, so knowing who and where your family lived is very important.