Petunia Dursley is Harry’s aunt, a thin, blonde woman with a long neck who enjoys gossiping. Petunia’s sister Lily was Harry’s mother, and Petunia and her husband Vernon took Harry into their home after he was orphaned.
Petunia bullies and neglects Harry whilst indulging her spoiled son Dudley. Like Vernon, Petunia despises anything that is out of the ordinary, particularly anything to do with the wizarding world.
Petunia spends the day cleaning and cooking in preparation for the dinner with Mr and Mrs Mason. She forces Harry to do chores while she prepares roast pork and a huge pudding of whipped cream and sugared violets.
Petunia, Dudley and Vernon entertain Mr and Mrs Mason for dinner. When they hear a loud crash coming from the kitchen, Petunia follows Vernon into the kitchen to see Harry covered in her carefully prepared pudding. Petunia fetches ice-cream from the freezer to replace the destroyed dessert. As she hands round after-dinner mints to her guests in the dining room, a large barn owl swoops in through the window and drops a letter on Mrs Mason's head.
Three days later, the Dursley's show no sign of relenting with their plan to prevent Harry returning to Hogwarts at the end of the summer holidays. Petunia delivers Harry his meagre portions of food through the cat-flap fitted onto his bedroom door.
Petunia is as nervous as her husband that Harry might reveal his 'abnormality' during Aunt Marge's stay. On the last night Petunia prepares a fancy dinner finishing with lemon meringue pie. She starts to look tense when Marge begins asking questions about James Potter.
After reading the pointed comments of the Smeltings school nurse in Dudley's end-of-year report, Petunia is forced to acknowledge what she has previously refused to see: that Dudley has reached roughly the size and weight of a young killer whale. She instigates a family-wide diet at Number 4, Privet Drive, and rids the house of all of Dudley's favourite sweets and snacks. She attempts to keep Dudley's morale up by ensuring that her son still gets larger portions of food than Harry.
Petunia is unhappy about the impending arrival of the Weasley family at her house. She refuses to eat lunch that afternoon, and sits with her arms folded, looking as though she is biting back a furious diatribe she longs to throw at Harry. Petunia peers out of the window every few seconds as it gets nearer to five o'clock, and compulsively straightens the cushions in the living room. She is petrified when she hears noises coming from behind the fireplace, and backs up against the wall. When Arthur Weasley blasts through the fireplace, Petunia shrieks and falls backwards over the coffee table. She is silent as Arthur tries to make conversion, and cowers next to her husband.
Petunia screams when she sees what Fred Weasley's sweet has done to Dudley's tongue, and hurls herself onto the ground next to him when Arthur attempts to magically correct the Engorgement Charm, shielding Dudley from the wizard. She seizes the end of Dudley's swollen tongue and attempts to wrench it out of his mouth. She sobs hysterically as she tugs at the tongue, horrified at what is happening to her son. Dudley's tongue reaches four foot in length before Petunia and Vernon finally allow Arthur to shrink it.
Vernon and Petunia discuss Harry as they watch the news one afternoon during the summer. They are suspicious that Harry keeps trying to watch the news. The Dursleys hear a loud cracking noise coming from the street outside their house, breaking the silence on the street like a gunshot. Petunia screams when the noise occurs, and shrieks even louder when Harry jumps up and hits his head on the open window frame.
Petunia is suspicious as to why Harry was lurking under the window, and doesn't believe Harry's claim that he was trying to listen to the news. She warns her husband to be quiet when he begins to rant about 'Harry's lot', and calls her nephew a liar when he says that the wizarding world does make it onto Muggle news. The Dursleys think that Harry gets his wizarding news by owl, and don't believe his claim that the owls haven't brought him anything over the summer.