She’s done that, most recently in February (that I know of):
“You won’t find my family members on any rolls, and I’m not enrolled in a tribe. And I want to make something clear: I respect that distinction,” she said to applause from a Native American audience. “I understand that tribal membership is determined by tribes — and only by tribes.”
She went on to recount her family story, in convincing detail.
https://www.nytimes.com/2018/02/14/us/politics/elizabeth-warren-trump.html