Petunia Dursey was a squib. Seemed that most of the Evans family was. They didn't mind however as they readily accepted the muggle world, and held the general opinion that the magical world was in many ways ass backwards. More so when it came to the so-called purebloods. It came as no surprise when her younger sister Lilly committed accidental magic at age 7, and received her letter from Hogwarts on her 11th birthday, along with their friend Severus Snape. Lilly and Severus went off to the magical world at Hogwarts, while Petunia continued in the muggle world. She was working on her masters degree when she met the big jovial Vernon Dursey at a party her sister was having. It was love at first sight and soon they were married. Lilly and Petunia both had a son around the same time, and subsequent moves to new homes kept them from visiting as much as they would like. However the two sisters still talked to one another on the phone frequently. The Potters, despite being an old pureblood family, were not as ass backwards as some of the wizarding population and embraced such twentieth century conveniences as the telephone.
Although Vernon knew his friend James Potter was in law enforcement, he thought James worked for Scotland Yard and then later transferred to MI5. This was actually a cover story for wizards who worked for the Department of Magical Law Enforcement and the Aurors. Being a squib, Petunia knew the truth about James true employer, but the cover story was necessary to keep from breaching the Statute of Secrecy that for the most part kept the Muggle and Wizarding worlds in England apart from one another. Petunia also knew about the rise of the dark wizard You-Know-Who, James' efforts as the lead Auror on the Voldemort case, and the risks that entailed. She listened to her sister's concerns about how the ministry was letting Albus Dumbledore and his "Order of the Phoenix" take a greater role in the Voldemort case, and James' misplaced trust in the headmaster's well-intentioned, but somewhat incompetent handling of things.