Although Margaret Erskine had married Robert Douglas there is evidence that James V may have considered arranging their divorce and marrying his mistress. It seems that James or one of his advisors sought the advice of the Pope in the matter in June 1536. Shortly before James V finalised his marriage contract with Madeleine of Valois in November 1536, Charles, Bishop of Macon and French ambassador at the Vatican, wrote discussing his audience with the Pope. The Bishop had told the Pope that James never intended to marry Margaret and the petition was an imposture. The Pope replied that he had postponed any grant, thinking that the proposal was made without the King's knowledge. Chronicle accounts and English letters also mention this scheme and the involvement of James Hamilton of Finnart. One of the English ambassador Sir William Howard's informants was Margaret Tudor, and he reported to Henry VIII;
"Sire, I hear, both by the Queen's Grace your sister and diverse others that the marriage is broken between the King's Grace your nephew and the Monsieur de Vendôme, and he will marry a gentlewoman in Scotland, the Lord of Erskine's daughter, who was with your Grace the last summer at Thornbury; by whom he has had a child, having a husband, and his Grace has found means to divorce them. And there is great lamentation made for it in this country as far as men dare. Sire, there was no man made privy to this matter but Sir James Hamilton."
Had the marriage gone ahead, their son James Stewart, the future Regent, could have been declared legitimate. By July 1536, the Imperial ambassador in London, Eustace Chapuys, and Spanish diplomats at the Vatican believed the marriage had already taken place.
Later years
Her son Robert Douglas was sent to England and Cambridge University in 1560 as a hostage for the Treaty of Berwick. She became the keeper of Mary, Queen of Scots at Lochleven castle in 1567, with her eldest son William Douglas, later Earl of Morton. In the 1570s Margaret Erskine looked after her granddaughters at the New House of Lochleven and kept up a correspondence with their mother, Agnes Keith, Countess of Moray. Agnes Keith sent her gifts of "aqua vitae", a form of whisky. In January 1570, she wrote that Lochleven Loch was frozen, and her son was in the "Loich", the old castle on the lake island, because he was keeping the Earl of Northumberland, who was a fugitive from the Northern Rebellion. In June 1571, she wrote of her health and complained that Agnes, her daughter-in-law had not visited;
"Ye sall onderstand that I have beyne wery extreme seik baith in my bodye and stomak, and with ane sair leg, quhairoff am nocht throichlie conwelleseit as yett... I wald skarslie have belevit ye would have bene neir hand and veseit me nocht, and frindis heir."
