My knowledge is mostly with Canadian Indigenous people, but DNA test helps a lot with locating Indigenous ancestors.
Just a quick history lesson which might solve why she is listed as 'white' when you think she might not be. The first obvious answer is that she wasn't Indigenous, and this happens all the time. The second was that she face a form of oppression which made the idea of passing off as white the better alternative. Remember it was sometimes illegal (at least here in Canada through our Indian Act), and definitely discourage usually through violence for Indigenous peoples to enter white society as an equal in the mid colonizing stages of North America. Just keeping in mind that religious conversion and societal acceptance are two different things.
In Canada we experienced the 60s Scoop, which was when the government would take away Indigenous children from their biological families usually without any crediable reason other than race, and put them into foster care. Some of these children were adopted/sold into white Canadian families, American families, Australia families, etc. Sometimes these adopted families would not tell the child about their heritage. I think a similar event happened in Australia. I am not sure if this was the same for the United States, but it is worth checking out. I know America has an amazing National Museum for their Native American history, and you could probably look around on their website for more information on Indigenous peoples and their history in your region. Trust me knowing the history of the region for Indigenous peoples helps a lot when trying to connect an ancestor back to their traditional heritage!
Back to the DNA helping. My maternal great-grandparents were considered 'full status' (systems work a bit differently here in Canada, it would be the same idea as the American blood quantity), but I still match up with many of my Indigenous relatives. The family, and communities I am from are pretty much all connected through blood or marriage, but in your case I am guessing (if she was Indigenous) either adoption or major displacement (when the government wanted Indigenous land usually they were displaced, this is why knowing the history of the region is so important).
Sorry for the super long post, and I really hope this helps I have met a lot of genealogists who are just in it for the novelty, and don't due the culture justice. Just the way you are handling all these answers shows me that you really just care about the heritage and not the care.