Which actress won an Oscar for playing an actress who misses out on winning an Oscar?

California Suite is a 1978 American comedy film directed by Herbert Ross. The screenplay by Neil Simon is based on his play of the same title. Similar to his earlier Plaza Suite, the film focuses on the dilemmas of guests staying in a suite in a luxury hotel. Maggie Smith won the Academy Award for Best Supporting Actress for her performance as Diana Barrie in the movie.

In Visitors from London part of the film, Diana Barrie is a British actress and a first-time nominee for the Academy Award for Best Actress, an honour that could jumpstart her faltering career, although she knows she doesn't have a chance of winning.

Dame Margaret Natalie Smith, CH, DBE (born 28 December 1934), known as Maggie Smith, is an English actress. She has had an extensive, varied career in stage, film and television spanning over sixty years. Smith has appeared in over 50 films and is one of Britain's most recognisable actresses. A prominent figure in British culture for six decades, she was made a Dame by Queen Elizabeth II in 1990 for services to the performing arts, and received the Companion of Honour from the Queen in 2014 for services to drama.