Jess is a teenage girl. She is Mary's daughter, and is from her previous marriage with Kevin. She has a younger sister who is so far unnamed. Her parents are divorced and split custody of her equally, though they spend far more time with their father due to Mary's time spent working.
She has a history of messing with her younger sister; Mary chastises her for trying to scare her sister with the "Bloody Mary" ritual.
She is a lesbian (or bisexual) and is in a romantic relationship with Naomi.
In Bloody Mary, she and Naomi discover Mary's stash of phenobarbital. Naomi assumes it is alcohol and steals a bottle, later almost dying due sipping it. Jess expresses regret for letting her take it without knowing what it was and for snooping through her mother's things.