Napoli would have been her maiden name.
You will find women listed by their maiden name in death records as well.
You might find the death act of Filippa's husband in the "allegati" (attachments) to the marriage records. It would have been necessary for her to present to the official.
This marriage act does not identify her deceased husband.
Paolo was "celibe" - unmarried.
***EDIT TO ADD***
Here is the link to the Publication of the Banns of Marriage for Paolo Marino and Filippa Napoli.
At the bottom of this record (among the documents presented to the official) is noted the death act of
Emmanuele Di Maggio, first husband of Napoli, a copy of which was issued by the Cancelliere della Corte d'Assise[Crown Court] di Palermo, and gives his
date of death as 3 March 1879. He had been sentenced to imprisonment for 10 years.
https://familysearch.org/pal:/MM9.3.1/T ... ,352218601
AND....
Here is the
death of Orsola Mineo - mother of Filippa Napoli, and widow of Elia Napoli
Death on 9 February 1879
She was age 60 and born in S. Giuseppe Jato to deceased Giuseppe, and to deceased Filippa Pastore .
https://familysearch.org/pal:/MM9.3.1/T ... ,954438101
T.