She is one of the two unofficial Kingdom Keepers along with her "sister" Amanda. Their goal is to stop the Overtakers from controlling the parks.
Jessica was born in Maine being a Fairlie, meaning she had special abilities other humans didn't have. In her case she can dream the future events. When the military started studding she and sent her to a special house, Jessica escaped with her friend Amanda and got to Orlando where they lived in an abandoned church.
Here she was put on a spell by Maleficent so she could work for her and lure Finn to the Overtakers. She was saved by Finn and teamed up with the Kingdom Keepers and helps them in their duty to save the magic from the parks.
She was again kidnapped by Maleficent in the second book, but saved again by the keepers. In the third book, she and Amanda were turned into DHI's to help them in their nighttime missions.
- Jessica's backstory is almost similar to Wolverine, both are super-humans who were experimented on by the military but escaped and later joined heroic groups.