|This article centers around Jessica DiLaurentis, a book character. For another version check out Jessica DiLaurentis, a TV character.|
Jessica DiLaurentis (née Day) is the mother of Jason, Alison, and Courtney DiLaurentis. In "Heartless," it is revealed that Alison and Courtney were sired by Peter Hastings, the father of Spencer and Melissa. Before the DiLaurentis family moved to Rosewood, their last name was "Day-DiLaurentis," but they changed it because of their secret daughter, Courtney.
Jessica is blonde and blue-eyed with a svelte figure and a heart-shaped face like her daughters. Her hair is styled in shaggy layers.
Jessica DiLaurentis and her husband Kenneth attended the same law school, Yale Law School, as Veronica and Peter Hastings. Jessica had an affair with Peter around the same time he and Veronica had tried to conceive Spencer. At the time the twins were conceived, it is presumed that Veronica's surrogate, Olivia Caldwell, was already pregnant with Spencer since she was born around two months before Ali and Courtney. Peter only found out about the children after they were born. He had a blurry picture of Jessica seven months pregnant tucked away in his home office.
The DiLaurentises originally lived in Connecticut until the girls were about 7–8 years old. Courtney had forced Ali underneath the water of their swimming pool (may not be true since it was divulged to the girls by Real Ali) and their parents were horrified by the fact that they had a mentally unstable child. They eventually moved to Rosewood, where Courtney was quickly placed into the Radley, a mental institute, and the family pretended there were only two children. It is unknown why exactly Rosewood was chosen as the desired place to reside, but it certainly wasn't coincidence that the DiLaurentises ended up living on the same street as the Hastings. They were even next-door neighbors.On the night of Ali's disappearance, Jessica and Peter were together on Spencer's porch. Presumably they resumed their affair sometime after she and her family got settled in.
When the Radley was closed, Jessica and Kenneth had to send Courtney to a new institute. They chose the Preserve at Addison-Stevens, a lush clinic located near the border between Pennsylvania and Delaware. Courtney was extremely upset and didn't want to go. She managed to successfully fool her mother into taking her sister to the institute instead. It is rather odd that Jessica didn't notice anything amiss: though the twins were supposedly "identical", there were some subtle differences in their faces (Ali had a slightly thinner face, Courtney's was more heart-shaped) that any parent should have recognized. Regardless, she took the wrong daughter to the institute, unwittingly changing the lives of the entire family forever.
When Ali doesn't show up from the sleepover, Jessica remains fairly calm, asking her closest friends by phone if she was with them. However, when there is no sign of Ali, Jessica panicks and calls the police. She is also quick to send the real Alison, who was visiting that weekend, back to the mental institute. She and the family move out of Rosewood; when Ali's body is found three years later and Ian is the suspect, they move to neighboring town Yarmouth for the trial.
After a construction worker is found to be the killer, Jessica decides to make a public announcement about the existence of "Courtney" DiLaurentis. She fusses and worries over Courtney, who seems annoyed by her mother-henning. When Rosewood finally learns of the truth behind Ali's death, she and her family flee Yarmouth. In Ali's Pretty Little Liars, it's revealed that the family knew from the get go that one daughter killed the other, but they didn't realize the girls were switched.
It is hinted that Kenneth knew the truth about his daughters' paternity and fought constantly with Jessica. The real Alison noted that she was surprised they had not gotten a divorce yet. It is uncertain if Courtney or Jason knew, though the latter most likely came to his own conclusions on the matter.