The young British actress plays the daughter of Anne Hathaway's character, tragic prostitute Fantine, in the movie musical, and was set to join the rest of the cast at the ceremony.
However, Allen was taken ill with a nasty bout of influenza on the day of the awards show and vomited before she was due to get in a car to travel to Los Angeles' Shrine Auditorium, according to The Hollywood Reporter.
The youngster persevered and headed to the venue, but she was sick again in the vehicle and on the red carpet, so she left the prizegiving to recuperate.
Allen missed the chance to celebrate with Hathaway, who landed the Outstanding Performance by a Female Actor in a Supporting Role trophy at the ceremony, which was blighted by illness.
French actress Marion Cotillard refused to get close to reporters on the red carpet as she was sick, while Jennifer Lawrence struggled through a bout of walking pneumonia to pick up the Outstanding Performance by a Female Actor in a Leading Role prize for her performance in Silver Linings Playbook.