The correct answer is - her concern with a party instead of Mr. Bunbury’s health.
Oscar Wilde's The Importance of Being pokes fun at the Victorian society which placed too much importance of irrelevant things. He is using the character of Lady Bracknell to depict this mockery - she is concerned with her party going splendidly instead of worrying about another person's health. The frivolousness of her concern is similar to the general spirit of the Victorian era.