She made a promise to Dumbledore As Lily's last remaining blood relative, if
In Harry Potter and the Half-Blood Prince, after Petunia receives a Howler from Dumbledore, she tries to save Harry's life by allowing him to stay at their Privet Drive residence. She goes as far as defying Vernon, who wasn't for this decision.
She married a Muggle, Vernon Dursley and they had a son, Dudley. However, when Lily was murdered by Voldemort, Petunia became guardian of her nephew, Harry Potter, who was only an infant then.
The charm was ultimately sealed when Lily's blood-relative and sister Petunia Dursley took Harry into her house. This prevented Voldemort from hurting Harry until the day he turned seventeen, or when he could no longer call the house at Privet Drive his home.
From sisters to strangers
No doubt Petunia would have been saddened by the news of Lily's death but those complicated emotions – grief, regret and unresolved jealousy – were probably buried in the distractions of housework, gossip and pandering to her son Dudley's every whim.
Petunia's disdain for Harry was most likely born from a long-standing jealousy of her magical sister, Lily. A Howler from Dumbledore, addressed to Petunia, said 'Remember my last' – no doubt referring to the letter which he left with baby Harry, on the doorstep of Privet Drive.
Petunia wanted to be a witch: Rowling reveals that, “Petunia had some latent feelings of guilt about the way she had cut Lily (whom she knew, in her secret heart, had always loved her) out of her life.” She also says that Petunia always held out hope that she would show signs of magic “and be spirited off to Hogwarts.”
The fan asked the author if Aunt Petunia was a Squib (a non-magical person who is born to at least one magical parent) and Rowling replied: "Good question. No, she is not, she is not a Squib. She is a Muggle.
Petunia never showed any love and affection at all towards Harry because he reminded her of Lily and the wizarding world. She treated him as a waste of space, giving him the cupboard under the stairs at first and making him do all the chores. She, along with Vernon, ignored most of Harry's birthdays.
Her last line there is, "You didn't just lose a mother that night in Godric's Hollow, you know. I lost a sister." Since Aunt Petunia usually prefers not to acknowledge Harry's mother at all, it's a surprisingly sweet moment. In the book, she uses her last words to say "Well — goodbye" to Harry.
Dear Petunia, It is with great sadness that I must inform you of the death of your sister and her husband. They were murdered by a Dark wizard known as Lord Voldemort, whose cruelty and violence they had been fighting for years. I tried my best to protect them, but, alas, I regret to say that I failed.
Lily Josephine Evans (30 January, 1960–31 October, 1981) was an English Muggle-born witch, a daughter of Marion Evans and John Evans, the younger sister of Petunia Evans and elder twin sister of Willow Evans.
Vernon's dislike of Harry, she adds, “stems in part, like Severus Snape's, from Harry's close resemblance to the father they both so disliked”.
Petunia was incredibly jealous of Lily's magical ability and hated that her magical sister always seemed to be the centre of attention. When she married Vernon, she didn't want Lily to be a bridesmaid because she was tired of being overshadowed by her.
Today, both Tendler and Mulaney announced on their separate Instagram accounts that Petunia, who was in their 2014 wedding and would reportedly have turned 10 this June, has died. Tendler wrote the following: “Rest in peace my sweet Petunia.
Figg is a Squib and a member of the Order of the Phoenix. Apparently, she was stationed to live near Harry in order to keep an eye on him and the Dursleys.
J.K. ROWLING ALMOST GAVE HIM A MAGICAL CHILD
Rowling talked about how she almost gave Dudley a magical child himself. She considered having him be at Platform 9 ¾ during the epilogue. However, she decided not to do so because she thought Vernon's DNA would have killed out any trace of magical blood.
Though nominally a Muggle-born witch, Hermione is descended from the Dagworth-Granger family through her father's squib heritage.
Uncle Vernon and Aunt Petunia have both tried to physically abuse Harry. In the Order of the Phoenix, Vernon attempts to strangle Potter after he thinks he's done magic, and, in the Chamber of Secrets, Petunia tries to hit Harry in the head with a frying pan, which the wizard luckily dodged.
Dumbledore explained that he decided to leave Harry with Vernon, Petunia, and Dudley Dursley because of the blood wards. IMHO, I think he could have gone with some other way to keep Potter safe. I talk more about this here and here.
It is a specifically a school of magic, and Petunia had none. Imagine if Dumbledore had somehow let her in. Her life would be miserable, and she wouldn't really be able to participate in most classes.
He defended Harry because he feared the emotional repercussions that he would impose upon himself if he didn't; the Dursleys defended him because they feared retribution.
Of course Rowling later fleshes out Petunia's character, explaining to readers that Petunia desperately longed to go to Hogwarts, even penning a letter to Dumbledore asking for admission.
Dudley, on the other hand, reunited with Harry a few times so that their children could play together. Their relationship was awkward, but this was a major change from when they grew up.
Rowling adds that Vernon hated Harry because he saw father James in him, much in the same way that Snape does. "She did it grudgingly, and spent the rest of Harry's childhood punishing him for her own choice," Rowling explains.