Sorry, I don't know the answer to that one.If you suspect your grandmother was Indian, I would write to the Oklahoma History Center (they have a website), and the question to them would be:
Could you determine if my grandmother,give her name, was on the Indian census?Also give them as much information about her as you know (birthdate, where was on 1900 census, fatehr's name, etc.).
If she were on the Indian Census, then ask for a copy of the census card.The census card hopefuly will provide informatoin as to her parents, etc.
This is a hit or miss thing, but might be helpful.
If OHS determines that she was part Indian and identifies the tribe, and if you knew what town she lived in/near, then youmight contact that tribe to see if they have records of the schools back in those days.
This is a long drawn out process, but it is the best I can offer.