Rebel was born in Sydney, Australia and later lived in South Africa for a year. When she lived there, she contracted malaria. Malaria caused her hallucinate and in one of her hallucinations she had a vision that she was an actor and won an Oscar. It was after that that she decided to become an actor. Before then she thought she might be a mathematician.
In the movie Bridesmaids, Rebel's character lives with Matt Lucas' character. After they shot the film, they decided to move in with each other in real life because they had so much fun together on set. According to Rebel, they often get noise complaints for singing show tunes late at night.