Jill is a nine-year-old freak that appear in Lies and Plague.
She has the power of essentially enchanting people when she sings. Jill also had an older brother who was a normal somewhat sided with the Human Crew, although he's never declared as a member and he tries to protect her when they break into their home in Lies. he fails to save her and she was dragged away and threatened by the Human Crew, who put masking tape around her mouth and scrawled 'FREAK' on her forehead. They left her in the street where she wandered around for a few hours until falling into the hole that Brittney/Drake dug from their way out of the grave. This is also the book she was introduced in.
Sam found her and dragged her up, then took her to Mary 's daycare, but since she is 9 she couldn't stay there for long (the maximum age is 5). Before she has to leave, Orsay and Nerezza arrive and "adopt" her.
Nerezza refers to Jill as "Siren" and, at the very end of the book, when Sam was on the verge of destroying Drake Merwin, Nerezza made her sing and distract everybody, giving Drake time to regenerate. Her singing was then drowned out by the sound of the Brattle-Chance children arriving by helicopter with Sanjit as pilot.
Jill's ultimate fate is unknown. She might have died in the Lake Tramonto massacre or she might have escaped the FAYZ.
Her power was first noticed by her brother when she was singing the theme song of "The Fairy Odd Parents."