She does not like Nikki because in Tales From a Not-So-Fabulous Life, Nikki opened an invitation that was supposed to be Jessica's, even though Nikki didn't even know her at the time and did it by accident. Jessica works in the WCD office as an office assistant.
In Dork Diaries 9,she made fun of Mackenzie by watching a video of Mackenzie freaking out because she had a bug in her hair. Then, she wrote a letter to Miss-Know-It-All saying if she should still be friends with Mackenzie or take her place as CCP queen. She and Mackenzie got in a fight in the Girl's Bathroom and is no longer friends with her.
In book 10, she decorated MacKenzie's locker and turned it into a "We Miss you MacKenzie" shrine, so it may mean she still has feelings for her.
Jessica has long straight blonde hair that reaches her shoulders. She seems to wear pink and accessories a lot. Jessica is most likely a lip gloss addict, being a friend of MacKenzie's. She wears designer outfits similar to Mackenzie's and shops at the expensive stores at the mall.
Like MacKenzie, Jessica also tries to ruin Nikki's life by being MacKenzie's assistant and helping her humiliate Nikki. MacKenzie and Jessica had a lot in common. Jessica also acted as part of MacKenzie's "posse" meaning she was a follower rather than a leader. She was often seen gossiping and giggling with Mackenzie. MacKenzie and Jessica are both fashion snobs, being rich and popular. Jessica is a part of the CCP (Cute, Cool and Popular) clique. Her and Mackenzie are very snobby and rude to other people, including Nikki, Chloe, and Zoey.
Despite being the most popular girl at school. Jessica is currently not dating anyone, however it may be possible she might have a crush on Brandon Roberts.