Sylvestra was born on Jersey in the Channel Islands to a long-standing pedigree family of that name. She showed an interest in acting at an extremely early age, enrolling at the Peggy Sharpe School in London, where she felt inhibited by her small stature, and, in 1968, when she made her television debut in a 'Doctor Who' story, had to lie about her age as she was just coming up to ten years old and the minimum age for juvenile players was twelve. Subsequent television roles followed, including as Fanny Price in a 1983 adaptation of 'Mansfield Park' with Peter Firth, though, in cult television terms, this was eclipsed by a commercial,still long remembered, for Heineken lager where, in a parody of 'My Fair Lady', she portrayed an upper-class girl being tutored for a cockney role by Bryan Pringle, success only coming when she drank a can of Heineken (which 'refreshed parts of the body other lagers could not reach' and enabled her to proclaim that 'the wa'er in Major'a was sal'ier than in Mal'a.') Married to actor Owen Teale since 2001, they live, with their two children,in Telegraph Hill, London, near to Goldsmith's College, where she has done some teaching. In 2008 she appeared on the West End stage with Kenneth Branagh in his generally well received revival of the play 'Ivanov'.