Father William de Brewes, Lord of Abergavenny, Brecon, & Ower Gwent, Seigneur de Briouze b. c 1144, d. 9 Aug 1211
Mother Matilda (Maud) de St. Valerie b. c 1138, d. 1210
Margaret de Brewes[1] was born circa 1177 at Abergavenny, Brecknock, Wales. She married Sir Walter de Lacy, Sheriff of Herefordshire, Lord of Meath, son of Hugh de Lacey, Lord Meath, Justice of Ireland and Rose of Monmouth, on 19 November 1200.[2]
Family
Sir Walter de Lacy, Sheriff of Herefordshire, Lord of Meath b. c 1172, d. Feb 1241
Cawley's Foundation for Medieval Genealogy (FMG) notes the marriage of Margery de Briouse to Walter de Lacy, but provides no date. FMG does give a date of death for Margery as aft. 1255, see
https://fmg.ac/Projects/MedLands/ENGLISHNOBILITYMEDIEVAL3.htm#MargeryBriouseMWalterLacy
Weiss, Frederick Lewis, "Ancestral Roots of Certain American Colonists", 8th ed, 2008, p 168 (177A-7 and 177B-7) clearly presents a marriage date of 19 Nov 1200, see https://www.ancestry.com/imageviewer/collections/49030/images/FLHG_AncestralRoots-0192?ssrc=&backlabel=Return. I have checked the two sources listed by Weis, but neither includes a marriage date or death date for Margaret.
I have found a website that purports to be a history of Ewyas Lacy maintained by local historians, see http://www.ewyaslacy.org.uk/aboutus.php
This site includes this: Walter de Lacy married Margaret [?Margery] de Braose [Briouze], the daughter of William de Braose of Brecknock, Lord of Bramber, in November 1195 [?November 1200], and his son and heir Gilbert de Lacy was born c.1205 [1196?] in Ewyas. see http://www.ewyaslacy.org.uk/-/Theme-de-Lacy-family-history/1000-s-1100-s-1200-s/rs_ewy_0201
While the comment lacks sourcing, Weis' marriage date of 1200 certainly seems to be a typo.