Aunt Josephine is a recurring character in the series. She is a very eccentric woman who becomes the Baudelaire children's guardian after the death of their parents.
While Aunt Josephine doesn't write a letter in the series, she is a character who is very afraid of everything. Her fear of everything leads her to live in a very strict and repetitive routine.
She has several quirky habits and idiosyncrasies that include:
* Her obsession with lists: Josephine makes numerous lists for everything, including what to do when the Count Olaf shows up.
* Her fear of anything that could possibly harm her: She is terrified of the dangers of everyday life and even the dangers of not being terrified. This fear leads her to make numerous safety precautions, often to the point of absurdity.
* Her inability to break her routine: Josephine is highly resistant to change and struggles to deviate from her normal habits.
Instead of writing a letter, Aunt Josephine tragically meets her demise in *The Reptile Room* when she jumps out of the window of her home (mistaking a snake for the Count Olaf), thinking she is safer on the ground.
Perhaps you are thinking of a different character from the series? If you can provide more information, I might be able to help you figure out the letter you're looking for.