Oxenham was born in France but grew up in Devon before the family moved to Cornwall when she was a teenager.
Oxenham was a keen actress and participated in school plays and local amateur dramatic productions in Cornwall.
[2][3] Since 2023 Oxenham played in the lead role of Carrie in the Disney+ superhero comedy series Extraordinary.
[6] Mike Hale in The New York Times praised her for the communicating beyond the grave scenes which “a lip-syncing Oxenham does to great comic effect”.
[8] In March 2024, she was nominated in the “Female performance in a comedy programme” category at the 2024 British Academy Television Awards.