For the majority of her lifetime, Isabel was the royal couple's only child and thus fourth in line to the throne. She was moved down a place upon the birth of her brother Charles Stuart, Duke of Cambridge; however, he died of smallpox after living only for a month, so Isabel was promoted back up to fourth in line. In 1678, Isabel was joined by another sister, Elizabeth, who was also short-lived. Her family had a portrait painted of her by Sir Peter Lely. In 1678 when Isabel was two years old, the Popish Plot led to her parents' being exiled to Brussels to stay with Mary. The royal couple were accompanied by Isabel and Anne. A report that her uncle King Charles was very sick sent the family hurrying back to England. They feared that the King's eldest illegitimate son, James Scott, 1st Duke of Monmouth and commander of England's armed forces, might usurp the crown if Charles died in their absence. Monmouth enjoyed the support of the Exclusionists, who held a majority in the House of Commons of England. Charles survived but, feeling the family returned to court too soon, sent James and Mary to Edinburgh, where for the next three years they stayed on-and-off in the dilapidated Holyrood Palace, while Anne and Isabel stayed in London on Charles's orders. The couple were recalled to London in February 1680, only to return again to Edinburgh that autumn; this time they went on a more honourable footing: James was created King's Commissioner to Scotland. Separation from Isabel caused her mother to sink into a state of sadness, exacerbated by the passing of the Exclusion bill in the Commons. Lady Isabel, thus far the only one of Mary's children to survive infancy, died of natural causes in March 1681, five months before her fifth birthday, at St James's Palace, the place of her birth. She was buried at Westminster Abbey on 4 March as "The Lady Isabella, daughter to the Duke of York. Isabel's death plunged Mary into a religious mania, worrying her physician. At the same time as news reached Holyrood of Isabel's death, her maternal grandmother, Laura Martinozzi, was falsely accused of offering £10,000 for the murder of the King. The accuser, a pamphleteer, was executed by order of the King. Four years after Isabel's death, her father succeeded as King of England.
