There is no picnic in von Arnim’s The Enchanted April. When the narrative ends, the four women vacationing at San Salvatore pack up and leave for London. But Mike Newell’s film ends with a picnic. For a discussion, see Picnicsonfilm.org. 
See Elizabeth von Arnim. The Enchanted April. London: Macmillan & Co. Ltd, 1922. There are several dramatizations: Kane Campbell. Enchanted April (1925). London Methuen, 1927; Harry Beaumont Enchanted April (1935). Screenplay by Samuel Hoffenstein Rya Harris based on Elizabeth von Arnim’s novel (1921)and Kane Campbell’s dramatization (1925). RKO Radio Pictures; Newell Enchanted April (1991). The screenplay by Peter Barnesis is based on Kane Campbel’s Enchanted April (1925) and Elizabeth von Arnim’s novel (1922); Michael Barber. Enchanted Aprilz (2003). New York: Samuel French, 2003. drama 2003