Yes, Jane Seymour did star in a silent film. It was a 1929 British silent film called "High Treason". She played the role of Mary Tudor, the daughter of King Henry VIII and Catherine of Aragon. The film was directed by Maurice Elvey and also starred Matheson Lang, John Stuart, and Benita Hume.
The Enchanting Jane Seymour: Delve into the Life of this Canadian-American Acting Icon!