“I was so nervous, I got my dad to read me the lines for two hours straight,” she said about the audition.
Child-Villiers’ role is “bratty, snarky and different from her on-screen kind and sweet sister”, she said.
She has already appeared in Apple TV’s The Lord of the Rings: Rings of Power.
“I was doing drama clubs and an agent came along, picked a couple people out and put them up for roles,” she said.
Child-Villiers is inspired by the likes of British actress Florence Pugh to “bring a lot of range, and do both comedy and emotional”.
The new series of Rivals is set to be released later this year.