For the uninitiated, Nina Stibbe is a beloved and very funny British writer best known for her first book, “Love, Nina,” a collection of letters she wrote to her sister during her stint in the 1980sworking as a nanny to the children of Mary-Kay Wilmers, then the deputy editor of the London Review of Books, and the director and producer Stephen Frears. In other words, Stibbe, a keenly observant 20-year-old, had stumbled into a gold mine. That book, first published in the United States in 2014, was later turned into a BBC television series adapted by Nick Hornby. Stibbe has since gone on to write several acclaimed novels and works of nonfiction.