Brittany is best-known for portraying Katherine Wentworth, the scheming younger half-sister of Pamela Ewing and Cliff Barnes, on the primetime soap opera Dallas (1981–1985, 1987).

In 1964, she starred as a blind girl named Minerva Gordon in a two-part episode of The Outer Limits, "The Inheritors", and appeared in the Western film Stage to Thunder Rock.

Cupito also appeared in the season-eight premiere episode of The Andy Griffith Show titled "Opie's First Love" as Mary Alice.

At the age of 15, after appearing in Yours, Mine and Ours, Cupito's childhood career came to an end and she concentrated on getting her education at Cleveland High School, Reseda, California.

That was followed by TV movies and series, such as The Amazing Howard Hughes (1977), The Initiation of Sarah (1978), Death Car on the Freeway (1979), The Dream Merchants (1980), and LBJ: The Early Years (1987).

[citation needed] Brittany appeared again as Vivien Leigh in the climax of the made-for-TV movie about the search for an actress to star in Gone with the Wind's film adaptation, The Scarlett O'Hara War (1980).

[3] This caught the attention of the producers of Dallas, who were searching for an actress to play Katherine Wentworth, the scheming half-sister of Pamela Ewing and Cliff Barnes.

She made a brief, final appearance on the series in 1987, which was plausible storyline-wise because Bobby's death and Katherine's turned out to be part of Pamela's 31-episode dream (i.e., season 9).

Later, as an adult, she appeared in seven episodes of The Love Boat, Hotel, Fantasy Island, Melrose Place, and the 1990s revival of Burke's Law.

[6]: 1010  and later hosted more than 100 episodes of the magazine show Photoplay, produced by Jack Haley Jr. Brittany guest-starred on such other series as Married... with Children; Murder, She Wrote; The Perry Mason Mysteries; Dear John; Sabrina the Teenage Witch; and The Nanny.

In the 1990s, Brittany appeared in independent films, including Riders in the Storm (1995), Legend of the Spirit Dog (1997), The Protector (1997), The Biggest Fan (2002), Mothers and Daughters (2006), and Americanizing Shelley (2007).