Osgerby represented Great Britain at two consecutive Summer Olympics, starting in 1980.

Osgerby became the British women's team captain in 1982 and held that position for two years until retiring after the 1984 Los Angeles Olympic Games suffering from an ongoing injury of tendonitis in both shoulders.

At her Olympic debut in Moscow she won the silver medal as a member of the British women's team in the 4×100-metre medley relay, alongside June Croft, Helen Jameson, and Margaret Kelly.

She is the twin sister of Janet Osgerby, who competed as a swimmer at the 1980 Summer Olympics and became the first identical twins to appear in the same Olympic final, gaining a place in the Guinness Book of World Records.

She represented England in the butterfly events, at the 1978 Commonwealth Games in Edmonton, Alberta, Canada.