Hillary is the youngest child of Pete and Diane, younger sister of Warren, and stepsister to Bert. She's been referred to as a "Mini-Diane," as she's a driven overachiever. Already the head of numerous clubs as a freshman, Hillary sits at the top of her class.
While Hillary is eager to skip ahead and be an adult and contributing citizen, she is still navigating high school life. She's busy balancing crushes, friend groups, being cool, and overachieving. Kate, who considers herself young and hip, often wants to bond with Hillary over these high school problems. But Hillary, who thinks she's smarter than Kate, is completely uninterested in being friends.