Sophie played the Sylvester McCoy's Doctor's assistant, Ace, from 1987 to 1989.
In 1987, she was cast as Ace in Doctor Who. Her tenure on the show spanned the last nine stories of the programme's original run, which ended in 1989.
Both before and since Doctor Who, Aldred has had a varied and busy television career, particularly in children's programming, where she has presented educational programmes such as Corners, Melvin and Maureen's Music-a-grams, long-running BBC series Words and Pictures and also CITV paranormal show It's a Mystery in 1996. She also played the character Minnie The Mini Magician from Series 8 onwards on CITV's ZZZap! between 1999 and 2001. Aldred has presented and sung in several BBC Schools Radio series, including Singing Together, Music Workshop, Time and Tune and Music Box. She has also performed on radio and in the theatre. She has also reprised her role as Ace in the charity special Dimensions in Time and the Doctor Who audio plays produced by Big Finish Productions. Throughout the 2000s she has worked extensively as a voice-over artist for television advertisements, and has also provided voices for animated series such as Bob the Builder and Dennis & Gnasher.