Margaret Beaufort
Lady Margaret Beaufort, Countess of Richmond and Derby (1443-1509)
Lady Margaret Beaufort had been married four times in her life, but is most mentioned with regard to her marriage with Edmund Tudor and being the mother of Henry VII.
At the age of 12 Margaret Beaufort was married to Edmund Tudor in 1455. The marriage did not last long, since Edmund was dead by November 1456, leaving behind his six-month pregnant wife. So on the 28th of January 1457 Margaret gave birth to her only son, Henry VII. From this point on Maragaret´s main interest was to keep her son safe. In order to do so she actively took part in deciding who she would marry next.
Sources
Janse, Sharon L. (2010). The Monstrous Regiment of Women. Female Rulers in Early Modern Europe. Palgrave Macmillan: New York.