Thank you for the information. I am a bit confused. On a separate post you can see the marriage record for this person. It appears that someone has gone back in and written in the last name of Lanza on the marriage record. Similarly, on her subsequent children's baptismal records, she is listed as either Benedicta or Francesca Lanza. Where do you think Lanza came from?
Lanza was probably invented by the town officials for an occasion where a surname was required and she had never had one. They would then go back and 'correct' any previous acts. The one you provided looks like a parish record and they probably didn't care that she had no surname. It would be the civil acts that would require one.
The surname given would be one that is not present in the town.* It would just be assigned. I have an ancestor who was an abandoned infant and this all came as quite a surprise to me as well. My ancestor still did not have a surname at the time of her wedding.
*Ann (Italysearcher) was the one who told me this.