Margaret de Clare - Verification of identity

Burke’s says nothing about her:

https://books.google.com/books?id=ZU59tRkdl2MC&lpg=PA877&ot...

I wonder if she’s been confused with this person:

http://fmg.ac/Projects/MedLands/ENGLISH%20NOBILITY%20MEDIEVAL.htm#M...

Thomas & his wife had four children:
a) MARGARET de Clare (-late 1333). The primary source which confirms her parentage and first marriage has not yet been identified. Inquisitions made after a writ dated 10 Apr "14 Edw II", after the death of "Thomas son of Richard de Clare", name "Margaret the wife of Bartholomew de Badelesmere and Maud the wife of Robert de Welle, aunts of the said Thomas and sisters of the said Richard are his next heirs and aged 30 or more”[1823]. King Edward III ordered the restoration of her lands to “Margaretæ quæ fuit uxor Bartholomæi de Badelesmere” by charter dated 22 Feb 1327[1824]. m firstly (1289) GILBERT de Umfraville, son of GILBERT de Umfraville Earl of Angus & his wife Elizabeth Comyn of Buchan (-before 23 May 1303). m secondly (before 30 Jun 1308) BARTHOLOMEW de Badlesmere of Badlesmere and Chilham Castle, Kent, son of GUNCELIN Badlesmere & his wife Joan FitzBernard of Kingsdown, Kent (-1322). He was summoned to Parliament in 1309 whereby he is deemed to have become Lord Badlesmere.

That Margaret de Clare is also described here:

https://www.findagrave.com/memorial/57715264

His wife’s name is not known, and changing it accordingly on Geni.

https://www.clanmacfarlanegenealogy/

At his death, Sir William Montifex left three daughters.
*1. Mary, married to Sir Johu Drummond of Stobhall, who got with her the lands of Cargill, Auchterairder, Kincardine, &c.
*2. Dornagill ; and,
*3. Margaret.

These last two were dissatisfied with the king's division of their father's estate, and fled to England to complain. Their inheritance was immediately forfeited, and the king gave Doraagill's portion of Pitfour and Dumgrum, to Duncan Napier: Pitcook in Perthshire, and half Kilmahew in Dunbarton, to William Napier: and Margaret's part to Hugh Danielston, whose successor was Lord Lyle. King David's gifts are dated at Dunbarton in 1366.

Erica,

I worked on this a bit and so far I now have the following:

William Sheriff Of Perthshire de Montefichet 1204-1241 married to Margaret de Montefichet (born De Clare Fitzgilbert)) 1163-1204 (notice the FitzGilbert

AND

William Baron Cargill de Montifex Montefichet 1305 -1366 who is now married to Mary de Montifex Montefichet (born Montieth) 1304-1333