While the current DNA tests claim to have markers identifying NA ancestry they do not identify a specific tribe or geographic area. It is not used by any tribes as yet for any membership application. (One tribe makes one take a paternal DNA test to be sure one is the bio child as claimed and listed on Birth Certificate from what I have read)
I have NA DNA and have traced with documented sources back to a NA Ancestor pre American Revolution, but because there are about 18 other ancestor lines, some with brick walls at 1880 or so I cannot say the DNA is from just this one ancestor (tribe).
Same with your friend...Unless she has her birth mothers line traced back and ruled out NA ancestors on maternal line she really has no "propf" of her father being NA. I don't believe any NA DNA can be determined to be from maternal or paternal lines.