[2] Cowper made an impression as a film actress in her early career, but she is best known for her work on British television, in particular her role as D.S Helen Diamond in BBC's Dangerfield.
Leading filmmakers David Puttnam and Francis Ford Coppola tipped Cowper "for the top" after she appeared in the American films Lionheart and Dreamchild— her performance in Dreamchild has been described as "excellent" and "impressive".
"[4] Cowper has since appeared in a variety of British television series, which includes: Inspector Morse (1991); Rides (1992–1993); Casualty (1992); Holby City (2000); The Bill; Devices and Desires (1990); as Deborah Wade in the BBC's Real Men (2003); as Edith West in The Grand (1998) and Judge John Deed (2007), among others.
She has also played the recurring character Gina Williams—the sister of Cindy Beale (Michelle Collins)—in BBC's EastEnders on four occasions—she first appeared in 1998, then returned briefly in 1999 and 2007, before reprising the role for the latest time in 2014.
Cowper was in a long-term relationship with Tony McCann, a convicted armed robber who served a 15-year jail sentence for holding up a Lloyds Bank and stealing £9,000 in 1988.