In the novel, she is a minor character hailing from Spain. She was unable to attend the farewell gala, due to her being suddenly ill (it was later explained that she wasn't actually unwell, just spoiled and temperamental). She later sings Faust and croaks like a toad
In the musical, she is a major character hailing from Italy. She is more selfish and spoiled, and she is courting the main tenor, Ubaldo Piangi, who panders to her.
In the 1943 and 1989 versions, she is killed by Erik.