Her husband had, about 1489 found means to be appointed one of the commissioners for collecting the King's rents in Orkney and Shetland, and some years later (1501) advanced a step towards regaining the Isles by obtaining a lease of the Earldom for a period of nineteen years. [From Barry]
Early in 1514 Lord Sinclair is noted as having sold to James IV, eight of the machines called serpentines, and their price, £100, was paid to his dowager in the same year after his death at Flodden. A notice in 1514 refers to the late Henry Lord Sinclair killed under the King's standard in the fields of Northumberland. It also mentions his fee "pro officio suo artilyearie", and the serpentines he had sold to the King. In the same year Lady Margaret as Custumar accounts for the customs of Dysart. In the second year of Lady Sinclair's widowhood, 1515, the Orcadians elected James Sinclair (natural son of Sir William Sinclair of Warsetter, Sanday) as their leader and virtual Governor, the possessor, though illegitimate, of most of the wealth of his family, and the inheritor-as a born and bred Orkneyan of all its popularity. On the plea of a general devastation by the English fleet in Orkney, they withheld Lady Margaret's Rents for three years (1523-25), and forced her son Lord William to surrender her castle of Kirkwall and escape into Caithness. [Balfour's Memorial]
On 17th April 1524, Confirmation issued to William Lord Sinclair and Elizabeth Keith his spouse, of Newburgh and the fishing of Eythan. He next appears as one of the Council of Nobles convened by James V on the escape of that monarch from the Douglases in 1528. [From Tytler]
Perhaps in return for his support he obtained from King James the Letter of Four Forms sanctioning the Invasion of Orkney in the following year to force James Sinclair to surrender the usurped governorship.
Forming an alliance with his near kinsman John, Earl of Caithness, they collected a considerable military force, and embarked for Orkney sanguine of victory, but sustained a crushing defeat at Summerdale, the Earl and 500 of his followers being slain, while Lord William of Ravenscraig and others were made prisoners.
It appears from a complaint of Lord Sinclair that James Sinclair had been guilty of excessive cruelty. Previous to the fight at Summerdale he slew several of his lordship's friends and attendants in the Castle of Kirkwall; and a week or two after the battle, among other atrocities, he put to death in cold blood thirty men who had fled for sanctuary to the Cathedral of St.Magnus and other places of worship in the country. It is stated in the complaint that he dragged there by force out of the church, stripped them naked, and then cruelly killed them "in his contemption of God and holy kirk, and breaking of the privilege of the Girth". [History of Caithness].
King James demonstrated his authority by renewing Lady Sinclair's rights till 1540, and in 1543, on the occasion of the suit instituted by the Queen Dowager against Oliver Sinclair of Pitcairn, William Lord Sinclair is found interposing a protest that whatever Oliver Sinclair had done should not prejudice his right to tack [lease] and assedation.
William, Lord "Sanchar", is one of the principal Scots nobility who agree in 1544 to support the authority of the Queen-Mother as regent of Scotland against the Earl of Arran, and declare him to be deprived of that office. [State Papers]
This Lord Sinclair married, first, in 1515, Lady Elizabeth Keith, relict of Colin, Master [heir apparent] of Oliphant, daughter of William, third Earl Marischall, by whom he had issue -