I don't watch much network television, so I'd not seen or heard of her before. When I first saw her, I knew that she had some African heritage. The reason I would call her white, or "white-presenting," is because it is a racist throwback to consider someone "black" because they have African DNA in some minute quantity somewhere. There is an actual term for someone who's 1/16th black, but how it can be other than "who the hell knows?" is a mystery to me.
Of course Markle is aware of her ethnic heritage. She was brought up by her mother. She has eyes; she knows what it's like to be black in America, beautiful, white-adjacent, or no.