Wikisimpsons - The Simpsons Wiki
While she has a sweet and calm appearance, Jessica also has a penchant for mischief and chaos, and can cross the line farther than Bart Simpson himself. Amongst boys smitten by her, she falls right into the role of femme fatale, and isn't afraid to use them.
She went to a boarding school, but was expelled for destroying school property, stealing collection money on Sundays and starting up fights with whomever she could.
She was also Bart's girlfriend for a while. According to Bart's experiences with her, she wasn't afraid to dare him to skate down an extremely steep hill littered with truck accidents, and even pulled the fire alarm during the school day out of pure thrills. He also states that she has an IQ of 108, and that she's "like a Milk Dud, sweet on the outside, but poison on the inside." She went too far, however, when she stole collection money again and pinned it on Bart. Lisa Simpson, however, brought her to justice. After showing the evidence that Jessica is bad, her father doesn't want to believe his daughter is bad and he continues to blame the theft on Bart. Later, Bart lets her take advantage of him
Despite the fact that she's a wicked, misbehaving girl, she does try to get attention from her father, who is seen not giving her a proper upbringing. But her father walks away like a coward rather than being a parent. She also explained that her behavior, in part, is because of her desire for attention for her father.
Bart has a photo of him and Jessica in his "Precious Memories" box.