[8] Some time after her first husband's death in 1626, she married Captain Henry Sibthorpe, who was an army officer then serving in Ireland.
[11] As a mock elegy, Southwell dedicates 120 lines to explorations of MacWilliams’ physical body, the state of her soul, the Ptolemaic and Platonic heavens, and religious devotion.
[12] Her internal colloquy begins in a specific address to MacWilliams’ bodily and spiritual experience, before she develops a broader description of the heavens and Catholic religious practices.
As a metaphysical elegy, Southwell creates an image of a Ptolemaic and Platonic universe in which prayer should be dedicated to the Holy Trinity instead of Catholic saints.
Southwell was apparently buried at St Mary's Church, Acton[13][14] and a plaque was mounted on the south wall.
[18] Of Southwell's daughters, Elizabeth, who married firstly Sir John Dowdall, and secondly Donough O'Brien, a younger son of the 1st Viscount Clare, is known for the spirited account she gave of her defence of Kilfinny Castle during the Irish Rebellion of 1641.