Elizabeth Warren is NOT attempting to establish tribal citizenship, but rather to simply answer the question of whether she has any Native American ancestors, which a DNA test can indeed prove.
Besides, if you look at the history of the Cherokee Nation you'll see that historically the criteria used to determine whether you were a member of a Cherokee tribe was a bit vague, to say the least.
First off, unlike some other Native American tribes, the Cherokee was actually a 'confederation' of many different groups of Indians from many different parts of Eastern and Southeastern United States. For example, in the early 19th century many of the Cherokee living in what would become the Confederacy, owned Black slaves. When Andrew Jackson ordered the forced removal of Native Americans, most of whom were Cherokees, from places like Georgia and other parts of the south, the tribes took their slaves with them to what would someday be the state of Oklahoma. After a while, most of these black slaves were accepted as full tribal members, marrying into existing Native American families. In fact, at one time, something like 10% of 'Cherokees' were of African descent.

OCU