Windsor was discovered by the writer and director of BAFTA-winning The Unloved, Samantha Morton, in a local drama school and casting agency, Rama Young Actors.

[1] Windsor attended the Nottingham Actors Studio, a not-for-profit CIC organisation, and the Television Workshop,[2] and has signed a contract with London-based talent agency, the Artists Partnership.

[3][4] Windsor's first professional acting role was in 2009 as Lucy Manvers in the television movie The Unloved at age 11.

In 2017, she played Holly Winshaw in the BBC miniseries Three Girls,[6] which was based on the Rochdale child sex abuse ring, and for which she won the 2018 BAFTA TV Award for Best Actress.

In 2017, Windsor was named as a BAFTA Breakthrough Brit, one of the 20 members from the film, television and gaming industries.