Jenna is a student in Daria's English/Language Arts class at Lawndale High. Her name can be seen on Timothy O'Neill's seating chart in "Cafe Disaffecto".
Based on her dorky and conservative clothing, she's presumably one of the 'brains'. She's got more of a social standing than Daria though, and seems particularly popular with boys: she's seen walking hand-in-hand with Josh during the Bridal Expo in "I Don't", apparently goes on a date with Adam ("I Loathe a Parade") and chats with "Tiger Guy" in "Fat Like Me". The aforementioned date was at the school homecoming parade, which she seemed to enjoy.
In the flashback to Mr. DeMartino's heart attack in "The Big House", Jenna is one of the very few students watching the ambulance with dismay and concern.
She's a fan of Mental in the Morning ("Jake of Hearts") and of high school American football ("The F Word").
Jenna in fanfiction
She's rarely appeared in fanfiction. One of her first known appearances was in Trapped by Jim North, where she appears mostly as a spider-infested corpse. It is significant however for giving her a fanon surname of "Schwartz".
She later appears as a lower card wrestler (and tag team partner to Cindy) in the Lawndale Fighting Championship series by The Excellent S.
She also appears as the President of the Anime Club in Quinn's Code series by Cfardell Brenorenz29. The surname Schwartz is also used in these series.