I used to read a book when I was a teenager in the 1970s called either Lissa (or perhaps Lisa). I am not sure if that was the actual title, but she was the main character in the book.  Lissa was found alone as a baby or toddler after the Great San Francisco earthquake, her parents were never found.  She is now in her late teens and living alone in San Francisco and working at a large department store. The owner’s son or a relative ends up falling in love with her.  They end up I believe by accident finding her real Grandmother and it turns out that Lissa is from a wealthy and influential family.  I am trying to find the title of this book and the author.  It was probably written in the 1950s or 1960s