How you laid this out is very cool. I knew most of these facts but hadn't woven them into a picture of Daphne.
From the evidence, it seems like Daphne and her family's culture is defined more by their education and liberal values than by where they live. Reading Beloved seems like something to try and get in touch with your heritage (as well as because it's good). So it seems like relating to Daphne more as a character from cultures I do know (i.e. not defined so much by being black) is reasonable.
(It's kind of how I am too - even though I'm half Indian, love my Indian relatives and would like to get in touch with my Indian heritage more, the indices of who I am are really much more my school, who lives near me, what websites I visit *ahem*, my age etc.
Not that I want to characterise by human nature - I don't - but I need to know I can get my head around the character.