Although her family was Anglican Protestant, Mary converted to Catholicism as an adult. This may have been one of the reasons why she gave financial assistance to her niece Arbella Stuart, who was also first cousin to the King, in 1610, with the knowledge that the latter was planning to elope to the Continent with her cousin William Seymour. This marriage was certain to enrage King James I of England, since William, like Arbella, had a respectable claim to the Throne (by most reckonings she was fourth in line to the Throne and he was sixth in line). For this, Mary was imprisoned in the Tower of London. She was tried for her role in the elopement, and was heavily fined, but not released. Later, Arbella accused Mary of being involved in a Catholic plot. Arbella's biographer remarks that Mary's motives in aiding Arbella are very difficult to understand: even allowing that Mary was a Catholic, and fond of her niece, she was certainly intelligent enough to understand the dire consequences for herself. Perhaps she relied on her husband's influence to save her from the Tower, and like her mother, she was one of the few women of the time who was used to getting her own way.