1.) (Fictitious character) Mary Cavendish is the wife of John Cavendish, the elder of the two stepsons of Emily Cavendish Inglethorp. Her husband inherited the house Styles upon his stepmother's death.
2.) Mary Talbot, Countess of Shrewsbury, née Cavendish, (1556–1632) was the wife of Gilbert Talbot, 7th Earl of Shrewsbury, who was her stepbrother. She was sent to the Tower and heavily fined for assisting her niece, Arabella Stuart, in her elopement with William Seymour. She was released, bur returned to the Tower after refusing to testify at an inquiry. She had five children but only her three daughters lived to adulthood. Francis Bacon is said to have remarked that while Lord Shrewsbury was no doubt a great man, there was one greater than he, his wife.Mary Talbot Countess of Shrewsbury in Wikipedia