Dumbledore’s Correspondence With Aunt Petunia
In the books, when Harry is collected by Dumbledore at the Dursleys, Dumbledore says to Petunia, “We have corresponded, of course.”
Harry thinks that Dumbledore is referring to the Howler sent to Petunia by Dumbledore in the fifth book.
However, we see in Snape’s memories that Petunia sent a letter to the Headmaster asking if she could also go to Hogwarts.