Trentham, who was born Barbara Lynn Schilling in 1944 in the Brooklyn borough of New York City, moved with her parents as a child to Connecticut.
She attended Mount Holyoke College in South Hadley, Massachusetts, from which she graduated in 1966 and then moved to England to study at the University of Oxford.
In 1976 she performed in the action drama Sky Riders and had a cameo in the British-German television series The Girl from Outer Space.
In 1980, while working in Los Angeles as a reporter and producer of Those Amazing Animals, she met English actor and comedian John Cleese at a Monty Python performance.
[citation needed] During her marriage to Cleese her love for art was reawakened and she began a third career as a painter, her preferred medium being oil paint.