Despite being English, she was cast by producer John Nathan-Turner as Peri, the first American companion on Doctor Who (1963). She kept her American accent on the series between takes and during interviews so that she wouldn't confuse the audience.
[speaking in 1985 about men's reaction to her as Peri in Doctor Who (1963)] I think it must be something to do with the sexy tight costumes I wear. They are so tight they are sometimes uncomfortable - that's why I like wearing baggy clothes away from the series.