She is definitely recognized as a Khandro by authentic lamas.
It does not appear that she is part of a federally recognized band of the Cherokee. It is highly political in Native communities in the U.S. who is viewed as a real Native American and who is not. There are 300 tribes currently seeking Federal recognition in the U.S. and that recognition is a huge financial boon for the tribes who get it. Recognized tribes have to determine what blood quotient tribe members have to be, such as 1/4 or 1/2. There is a lot of controversy over these issues, and also intermarriage with people from other cultures, and whether one lives on a reservation or not, whether one takes part in Pow Wows or not, and so on.
If she is a part of a tiny unregistered band (family) that wandered to Vermont, and doesn't keep contact with the Cherokee Nation, there is almost nobody in this country who is going to stand up for the validity of her band or her status as a Native American. This is understandable. Does that mean she does not carry an authentic tradition from her ancestors? I don't know about that.
She keeps a fairly low profile as a teacher--why put your gun sites on her? If you continue down the path that you have started on you'll find people who doubt the authenticity, ethics, or capacity of every teacher in Tibetan Buddhism.