Her parentage and marriage are referred to by Eyton but he cites no primary source on which this is based. 1
Marriage Information:
Unnamed daughter of Hugh DE LACY married Sir William III FITZ ALAN, Lord of Oswestry & Clun, son of William II FITZ ALAN, Baron of Oswestry, and Isabel DE SAY, Lady of Clun. (William III FITZ ALAN was born about 1154 in Oswestry Castle, Shropshire, England and died in 1210 in Clun, Shropshire, England.)
Sources
1 Foundation for Medieval Genealogy, Medlands: daughter.