I am a mystery fan. I second Stephanie's recs for the Donna Leon and Jacqueline Winspear books.
Another option would be a classic mystery by Agatha Christie.
The Bernie Rhodenbarr books by Lawrence Block are hilarious--about a burglar who solves mysteries.
Sara Paretsky writes some excellent but somewhat dark mysteries set in Chicago, with V.I. Warshawski.
I think one of the strongest women writers today is Marcia Muller, who writes the Sharon McCone series. Sue Grafton's alphabet mysteries with Kinsey Millhone are fun. Margaret Maron has a good series with Judge Deborah Knott.
Do you know what she likes? I will try to think of more writers.
Also, if she likes short stories, there are several volumes of Sisters in Crime short mysteries, which might help her find new-to-her authors.
For you to be here now, trillions of drifting atoms had somehow to assemble in an intricate and intriguingly obliging manner to create you. It's an arrangement so specialized and particular that it has never been tried before and will only exist this once.
--Bill Bryson, "A Short History of Nearly Everything"