Meet Tracey Davis. She's more just a name in the books, so here's the rundown.
Half-Blood Slytherin in the same year as the trio. Mom's a French witch, Dad was a Muggle, since died of cancer. She does medical potions research for the Ministry and is interested in looking at the components of muggle medicine and whether it can be used for any wizarding ailments.
Lines: other ministry workers, other Slytherins, people in medical fields or potions, other people she knows from Hogwarts or her time in Paris.