Jill came from somewhere outside London and she was in a large family. She had six older sisters and seven aunts. She was the "seventh daughter of a seventh daughter" which meant that, biologically, she was a witch and was born with supernatural abilities.
Before Jill was enrolled at Groosham Grange, she had a rocky upbringing. Her father was an extremely busy businessman and diplomat - so busy that when Groosham Grange told him she had been accepted, he jumped on a plane and went back to South America. Jill's mother was an actress, and was also so busy that she bumped into her daughter on the street and didn't even know who she was.
Jill had been expelled repeatedly from different academies and she was notorious as a troublemaker. However this difficult nature was due to her magical powers. She was sent by her parents to a finishing school but they were finished with her after she gave her cookery teacher food poisoning.
Jill's father was contacted by John Kilgraw, deputy headmaster at Groosham Grange, and Kilgraw told him that his daughter was enrolled. Jill's father immediately saw a new job in South America and flew off immediately. Jill was sent to Groosham Grange which was meant to be on a Norfolk island but no islands existed there.
On the train out from London, Jill first met David and Jeffrey Joseph, a fat outcast. Jill was stated to be rather sarcastic and depressed at this time, mocking Jeffrey's stutter. David became friends with Jill and realized they were all "difficult" kids.
David bonded with Jill during the ride to the school and was spooked out by Captain Bloodbath, the chauffeur, and Gregor, the deformed porter. Mrs Windergast, the matron, welcomed them and Jill warned David not to mess with her, despite her seemingly nice nature. Jill was taken to see John Kilgraw the next morning, where to her shock he pricked her finger and made her sign her name in her own blood.
Jill bonded with David over the next few weeks and he began to fall for her. Jill got used to David and they spent all their spare time together, and soon became almost a couple. However in their time together, they excluded Jeffrey, and this depressed Jeffrey and embittered him into joining the school, despite a promise the three had made - "Us against them." Jeffrey split up with David in an argument that day. Jill told David she was going to break out of school and tell police to get the mad place shut down. However her escape failed when Bloodbath caught her on his boat and dragged her off. Strangely though, she wasn't punished.
David burned his hand when exploring and Mrs Windergast gave him a witch's ointment to make him have a good time at Jeffrey's thirteenth birthday - although David did not know this yet. David did have a really good time, and danced with Jill, further strengthening their feelings, and David saw Jeffrey pick up a ring and join the school by slipping it on - he believed it was all a dream though - at least until Jeffrey was wearing the same ring the next morning.
David and Jill now contacted mainland Britain and the government to get the school shut down. An inspector did arrive, named Mr Weatherby, but Kilgraw killed him using dark magic when David slipped Weatherby a note to meet them at the cliff. David comforted Jill upon Weatherby's murder and they set out to escape a different way.
Finally, Mrs Windergast gave David a hint his time would soon come, and David decided to escape that evening. Despite Jill and David trying to escape together, Gregor accosted Jill, and Captain Bloodbath had his hands torn off while grappling with the boat rope which David drove away at high speed.
So David tried to alert police but no one believed him, so he began to research witches. He found Groosham Grange was actually a witch's school, where every witch in Britain had attended. Scared, he went down the town but saw Gregor, who had followed him, and chased him into a funfair, but the ghost train David hid in led him back to Groosham Grange. Confronted by the whole staff, David now hid in his room.
Jill was sent to find him and she greeted David, but too late David saw that Jill was wearing a ring, like Jeffrey - she was now one of them. She had been brainwashed into following them and had led David to Kilgraw and the others. Kilgraw explained how witchcraft was not as evil as human wickedness, such as bombs and murder, and how David could have a better life. Perhaps out of a desire to protect Jill, David agreed.
Return to Groosham Grange
Jill returns in the only sequel so far. Jill is attending the sports day at Groosham Grange, having fully adjusted to the school life by now. Jill is suddenly taking a fancy to Vincent King, a handsome newcomer, and David is angered by this because he sees Jill as his first girlfriend. David is about to start a fight with Vincent but then the obstacle race begins and David cheats, by tripping up Vincent. Jill sees, and is shocked by David.
On the cliff, David and Jill have a talk and Jill says how she feels about Vincent and David scoffs if she fancies him. Jill says its none of his business, and soon they almost have an argument and David tries to impress her with his own magic. Jill has become moody and will only reluctantly talk with David. David is worried about the coming exams and wants to become school champion and win the Unholy Grail - the source of all of the school's power. To get the Grail, David will do anything.
David sees Vincent up at the middle of the night, and tries all he can to pin the blame on Vincent - but to no avail. In fact, David gets the trouble.
Jill flunks her final exam and says it was awful. But then she warns an overconfident David not to be so sure, because Vincent also looks confident. Vincent has always been hiding in the North Tower of the school, making David suspicious of what he's up to in there.
Thinking Vincent is trying to steal the Grail, David fails his final exam, to his shock. Jill almost beats David and Vincent wins. But David and Vincent both have 666 points, so they almost both tie for first place. There has been a mix up with the papers and David suspects Vincent. In a tie breaker set at midnight at the British Museum in London, David works out that History teacher Miss Pedicure was an Egyptian mummy and finds her statue, effectively winning the Grail. But someone steals the statue and knocks David out by reanimating waxworks to hunt him down. David suspects Vincent does this, and tells Jill. Jill promises to keep an eye on Vincent but she somehow disappears.
Jill later reappears when David is knocked out by an adult's hand (confirming Vincent is not the thief) and she is angry at David for his incompetence. She blames David for all this and says that David suspected Vincent. David hears Vincent out and forgives him because he knows he's had a bad past. So now the only thing is to track down the true thief. A storm caves in on the island and the school is almost destroyed. David breaks them out (besides not using magic) and says they have to get off the island and follow the Grail. David works out his parents have the Grail because they were given the cup. So he follows.
Jill and Vincent bond over the time they try to shelter from the storm and almost fall for each other as a tsunami hits the school. David works out the traitor is Mr Helliwell, the Voodoo teacher, who stole the Grail because he had been brainwashed by the Church. Mr Helliwell is killed when he is crushed by a tower of Canterbury cathedral, and David takes the Grail back to the school. He then repents and decides to leave.
Jill has seemingly bonded with Vincent and they seem to be a couple in the closing pages. She says how she'll miss David.