In a fanfiction, Aunt Petunia could be a witch who was forced to suppress her magic by her parents who wanted to distance themselves from the wizarding world. When Harry comes to live with her, his presence slowly awakens her own magical side. She starts to have accidental magic surges and has to figure out how to handle them without drawing too much attention from the neighbors or Vernon.
One possible fanfiction could be about Aunt Petunia discovering her latent witch powers late in life. Maybe she starts having strange dreams that lead her to an old family heirloom that unlocks her magical abilities. She then has to deal with the shock of it all while also trying to keep it a secret from the Muggle world around her.
One possible fanfiction could be about Aunt Petunia having a strange encounter with a lemon - themed magical object. Maybe she accidentally uses it in a spell (in a non - canon, fan - created way) that makes her see a different side of the wizarding world she has always despised. This could lead to her having a change of heart about Harry Potter and his world.
One possible fanfiction could be about Petunia discovering her latent witch powers later in life. Maybe she stumbles upon an old family heirloom that unlocks her magical abilities. This could lead to a whole new dynamic in her relationship with Harry, as she now understands the world he belongs to on a deeper level.
Perhaps Aunt Petunia is a witch who was cursed long ago. The curse made her forget her magic and act like a Muggle. When Harry unknowingly breaks the curse, she suddenly has her powers back. She then has to face the wizarding world again and deal with all the changes that have occurred since she last remembered her true self. She might even have some unique powers that are different from the norm because of the curse.
Well, it could be quite strange. Maybe she's secretly a bit more interested in the wizarding world than she lets on. It might be a way for her to explore the stories from a different perspective, one that's not as judgmental as her usual self towards magic.
Aunt Petunia could discover a lemon tree in her garden that has magical properties. Since she's always been envious of the magical world (even if she doesn't admit it), she might try to use the lemons from the tree to gain some sort of power or advantage. For example, she could think that if she eats the lemons, she'll become more beautiful like the witches she's seen in Harry's pictures.
In a fanfiction like this, Petunia might start collecting wizarding memorabilia on the sly. She could have a hidden stash of things like old wizarding newspapers or even a broken wand she found. As she becomes more of a 'fan', she might use this collection to try and understand the world that Harry is a part of better, all while still maintaining her outwardly non - magical appearance to the rest of the Dursley family.
One possibility is that Petunia could use her witch powers to protect Harry secretly. Maybe she has a change of heart after years of resentment. She could have been in contact with the wizarding world all along, but hid it from everyone. This would add a whole new layer of mystery and family drama to the Harry Potter universe.
There could also be other characters from the original Harry Potter series popping up. For instance, Dudley might be in there, and his relationship with both Harry and Aunt Petunia could be explored further in the context of this fanfiction. And of course, depending on the direction of the story, some of Harry's friends from Hogwarts like Ron or Hermione could make an appearance, especially if the story involves the wizarding world interfering with Aunt Petunia's life.
She is very much concerned with appearances and normalcy. In the Dursley household, everything has to be in a certain order and conform to what she deems as a proper, non - magical lifestyle. This is part of the reason she is so resentful of Harry and his magical abilities.
The story could be different in that Aunt Petunia might become more empathetic towards Harry. If she reads fanfiction, she might start to see different interpretations of his situation and understand him better, which could lead to a change in their relationship at home.