Jennifer is one of Daria's classmates. Her name is known from "Cafe Disaffecto", thanks to a close-up of Mr. O'Neill's seating chart. She's actually one of three Jennifers in that class, and the only one that isn't Caucasian; one of the others is Burnout Girl.
She's been seen around the background character "Jade Hoodie"; the two might be friends. "It Happened One Nut" shows her hanging around at the mall with "Kia" and "Bib Overalls", other black girls in her year (though none of those three are ever seen around Jodie...).
Jennifer also has an interest in drama, signing up for The Canterbury Tales' auditions in "Fair Enough".
She's a fan of Mental in the Morning: when Bing and the Spatula Man turned up in "Jake of Hearts", Jennifer followed them on a circuit around the school and looked happy to be near them. In a fourth-wall destroying moment, she actually peeks out from behind Spatchula Man and grins, just like she's mugging for the camera... but the only 'camera' here is us. Was she aware we existed?
She appears as Jennifer Johnson in The Angst Guy's unfinished JÖRMUNGANDR; a Buzzdome employee after graduation, she takes evening classes at Lawndale State University so she can look after her father (who had a stroke) and younger sister when her mother's at work. She's familiar with Daria, who remembers her as "the tallest" Jennifer with a ponytail (she notes Daria doesn't ask if she was the African-American Jennifer).
In "God Save The Esteem", she appears in the See Jane Run AU as someone semi-popular jock who likes gossiping behind people's backs and is quite confused by Jane's morbid humour.