The princesses American guest. Princess Elizabeth has invited an American friend to the Royal Garden Party at Buckingham Palace, which takes place tomorrow (Tuesday). She is 18 years old, London born Marilyn Silverstone, formerly president of United Artists Pictures in England. Miss Silverstone was introduced to Princess Elizabeth at a children's party in London sometime ago. The Princess remembered the meeting and sent an invitation to the Garden Party through the American Embassy. Miss Silverstone arrived at Southampton at midnight last night (Sunday) in the 'Queen Mary ' picture shows, Miss Marilyn Silverstone, photographed on her arrival at Southampton.. 14 July 1946