Probably by mitochondrial DNA.
This could be a funny twist to the reparations movement. Most US blacks are more white than I am.
Mitochondrial? That would mean her pilgrim ancestor was a woman.
I think, though, you’re correct that it was DNA.
Through her paternal grandfather, she is a descendant of Mayflower pilgrim William Brewster.
And a significant number of them are descendants of slave owners. Black and white.
The issue of slavery undoubtably pre-dates recorded history. And, it's ugly history in this country is not quite the clear cut case that most believe.
History is riddled with little known, but inconvenient to some, facts.
1. And then there's the issue of blacks who were slave owners. Ten's of thousands of blacks owned slaves by the mid 1800's. Think of all the blacks in this country who are descended from BLACK slave OWNERS.
2. And then there's the issue of the first "legal" slave owner in the colonies (i.e. this country). Hint, he was black.
1654/1655 Virginia, John Casor (black) became a slave after having been an indentured servant. His "owner" was Anthony Johnson, a free black man of African descent.
Then, “About seven years later, Virginia made this practice legal for everyone, in 1661, by making it state law for any free white, black or Indian to be able to own slaves, along with indentured servants,”
https://www.smithsonianmag.com/smart-news/horrible-fate-john-casor-180962352/
https://encyclopediavirginia.org/entries/court-ruling-on-anthony-johnson-and-his-servant-1655/
3. And then there's the issue of the blacks in Africa that were key in the slave trade.
‘Africa’s Role in the Slave Trade Has Been Deliberately Forgotten… They Created a Myth That We Were Innocent,’ African Historian Says
https://caldronpool.com/africas-role-in-the-slave-trade-has-been-deliberately-forgotten-they-created-a-myth-that-we-were-innocent-african-historian-says/
The marxists/communists/progressives/racists in this country best not re-open that wound and pour salt in it by "giving" black people a taxpayer funded cash payout simply because of the color of their skin.