Question: Who is the mother-in-law of Agnes Leslie, Countess Of Morton?

Knowledge 1: Agnes Leslie, Countess of Morton
Agnes Leslie, Countess of Morton (born after 1541 – c. 1606) was a Scottish noblewoman, being the daughter of George Leslie, 4th Earl of Rothes as well as a direct descendant of King James II in her maternal line.She was the wife of William Douglas, 6th Earl of Morton, who as Laird of Lochleven Castle was the custodian of Mary, Queen of Scots during her captivity from June 1567 until her escape on 2 May 1568.Agnes was Queen Mary's chief female companion throughout her imprisonment; thus it was while Lady Agnes was recovering from childbirth that the queen successfully escaped from Lochleven. [SEP] Knowledge 2: William Douglas, 6th Earl of Morton
William Douglas, 6th Earl of Morton (c. 1540 – 1606) was the son of Sir Robert Douglas of Lochleven and Margaret Erskine, a former mistress of James V of Scotland.
Knowledge 1: Agnes Leslie, Countess of Morton
Agnes Leslie, Countess of Morton (born after 1541 – c. 1606) was a Scottish noblewoman, being the daughter of George Leslie, 4th Earl of Rothes as well as a direct descendant of King James II in her maternal line.She was the wife of William Douglas, 6th Earl of Morton, who as Laird of Lochleven Castle was the custodian of Mary, Queen of Scots during her captivity from June 1567 until her escape on 2 May 1568.Agnes was Queen Mary's chief female companion throughout her imprisonment; thus it was while Lady Agnes was recovering from childbirth that the queen successfully escaped from Lochleven. [SEP] Knowledge 2: William Douglas, 9th Earl of Morton
William Douglas, Earl of Morton (died before 1 November 1681) was a Scottish nobleman and Earl of Morton.He was the son of Robert Douglas, 8th Earl of Morton and Elizabeth Villiers.He succeeded as the 9th Earl of Morton on 12 November 1649.William tried to preserve the grant of the Islands of Orkney and Zetland which had been given to his grandfather, Sir William, 7th Earl of Morton.The wadset (a loan masked as a sale of land under right of reversion) of the Lordship had been set aside, and annexed to the Commonwealth in 1657.On the Restoration, he obtained a new grant, which confirmation was ratified by Parliament in 1661.However, this too was pronounced null and void, and the islands were vested in the Crown by Act of Parliament on 27 December 1669.Thenceforward the Earls of Morton held these islands under a form of mortgage from the Crown.On 9 September 1672 he resigned the Barony of Dalkeith in favour of James, the Duke of Buccleuch.The estate of Dalkeith and other lands, to the total value of £100,000 Scots yearly rental, had been sold circa 1643 to Buccleuch to enable the 7th Earl meet his expenses supporting the King.William married Grizel, daughter of John, Earl of Middleton, in 1662.Their only son, Charles, Lord Dalkeith, died in infancy in 1663.William died in 1681 leaving no heir, passing the Earldom to his uncle, James Douglas, 10th Earl of Morton who was the son of William Douglas, 7th Earl of Morton and Lady Anne Keith.
Knowledge 1: William Douglas, 6th Earl of Morton
William Douglas, 6th Earl of Morton (c. 1540 – 1606) was the son of Sir Robert Douglas of Lochleven and Margaret Erskine, a former mistress of James V of Scotland. [SEP] Knowledge 2: William Douglas, 9th Earl of Morton
William Douglas, Earl of Morton (died before 1 November 1681) was a Scottish nobleman and Earl of Morton.He was the son of Robert Douglas, 8th Earl of Morton and Elizabeth Villiers.He succeeded as the 9th Earl of Morton on 12 November 1649.William tried to preserve the grant of the Islands of Orkney and Zetland which had been given to his grandfather, Sir William, 7th Earl of Morton.The wadset (a loan masked as a sale of land under right of reversion) of the Lordship had been set aside, and annexed to the Commonwealth in 1657.On the Restoration, he obtained a new grant, which confirmation was ratified by Parliament in 1661.However, this too was pronounced null and void, and the islands were vested in the Crown by Act of Parliament on 27 December 1669.Thenceforward the Earls of Morton held these islands under a form of mortgage from the Crown.On 9 September 1672 he resigned the Barony of Dalkeith in favour of James, the Duke of Buccleuch.The estate of Dalkeith and other lands, to the total value of £100,000 Scots yearly rental, had been sold circa 1643 to Buccleuch to enable the 7th Earl meet his expenses supporting the King.William married Grizel, daughter of John, Earl of Middleton, in 1662.Their only son, Charles, Lord Dalkeith, died in infancy in 1663.William died in 1681 leaving no heir, passing the Earldom to his uncle, James Douglas, 10th Earl of Morton who was the son of William Douglas, 7th Earl of Morton and Lady Anne Keith.

Answer: Margaret Erskine