So, on topic…
The Cherokee nation’s first contact with Europeans was in 1540, and became a regular thing in the 1600’s. Thanks to the strange diseases brought by the Europeans, the Cherokee have been dying due to Europeans for hundreds of years longer than many other native tribes who lived further away from those early explorers, traders, and settlers. Often those who managed to survive through life-threatening illness were the “half breed” children who had some European genes in them. Also, thanks to location, the Cherokee gene pool further diversified with the addition of Africans (former slaves) as well.
Long story short, there’s no such thing as a 100% DNA Cherokee tribe member these days. That’s why the Dawes Roll and other documentary proofs are used: the point is whether or not your family has been treated like Cherokee over generations, not what is in your DNA profile.
In addition, geneticists can’t tell you which tribe you belong to via DNA. Even if you test positive for certain known markers, all it says is that you have Native genes in you, not which tribe or exactly how much of a percentage you are.
And finally, if your “100% Cherokee grandmother” was enrolled but in fact had only 1-3% verifiable Native DNA, you might not have any reasonable sized segments of that heritage pass down to you but she’s still your grandmother and she still grew up in the tribe with her family. Conversely (and this is the more common scenario), if your dark skinned grandmother’s family claimed to be part Native (to hide the fact one of her grandparents was an African slave, for example), you might grow up believing what your entire family told you but in fact when you do DNA testing you find out you have 3% West African heritage instead (or Italian, or Jewish…).
Basically, a DNA test will probably not give a definitive answer to the question. Doesn’t mean she’s lying. She might be telling the truth, or she might be telling the truth as it was told to her. She might even test positive for Native DNA, but it’s actually from a different tribe. It’s just not as conclusive as people think.
