Daphne is a witch in Harry’s year at Hogwarts. She took her O.W.L.s at the same time as Hermione (OP31).
Her younger sister Astoria grew up to marry Draco Malfoy (ITV, CC).
According to an early list of Harry's classmates that Rowling displayed during an interview (HPM), Daphne's name may originally have been Queenie Greengrass. If so (and this document can't really be considered canon), she is a Slytherin student from a pure-blood family (HPM).