Rooper was born in Hammersmith, London, England and is the daughter of TV journalist Alison Rooper. She attended Redcliffe Primary School in Chelsea, London and then, at age 12, went to Godolphin and Latymer girls' school. While working on The Famous Five she passed eight GCSEs with A* and A grades. From there she went to sixth form college where she got three A-grade A levels.