Note: On the basis of the following discussions, I am making Isabel a daughter of Philip Burnell & niece of Robert Burnell, Bishop of Bath & Wells. It could be that her father was another brother of Robert the Bishop.
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He [Robert de Scales] married Isabel.[l] He died before 4 September 1305. Isabel survived him and died before 26 July 1333. [Complete Peerage XI:499-500, (transcribed by Dave Utzinger)]
[l] G.E.C. states that she was of the family of Burnell, relying apparently upon Chester Waters (Chesters of Chicheley, vol. i, pp. 253-55), who cites the Scales Peerage Case, which, however, provides no surname. There are numerous references to Isabel under that name, but nothing has been printed which affords any proof of her parentage. From a note left by the late Miss Ethel Stokes, however, it appears that in the course of the claim for the right to the arms of Burnell (Lovell v. Morley, P.R.O., G.D. 26/69) in 1396 or 1397, it was stated in evidence that "in the church of Austin Friars', London, there was a chasuble with these arms, formerly in the nunnery of Blakebergh, and the ornament of a vestment with the same, formerly in the church of Middleton, which were given to the friars by a Dame de Scales, who was daughter of a Sieur de Burnell." Another deponent called her Isabel, said that she died about 56 years previously, and that the vestment lay on the tomb of the said Dame, which was in the said monastery, on her anniversary. Robert Burnell, Bishop of Bath and Wells, had had the wardship of her husband during his minority (Rot. Hundr., vol. i, pp. 16 1) 193), presumably having bought it from Clemence (see P. 499, note " n " above).
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Following copied from soc.genealogy.medieval newsgroup:
From: Cristopher Nash (enraq@@csv.warwick.ac.uk)
Subject: Re: Robert de Scales
Newsgroups: soc.genealogy.medieval
Date: 1998/08/15
I can only add that VCH-Herts ('Barkway'), 28, calls her Isabel Burnell, poss. relative (niece?) of Robert Burnell, Bishop of Bath & Wells, etc., and that Roger Scales (uncle of Isabel's husb. Robert) transferred to the bishop his life interest in Newsells Manor before the end of 1271 (Newsells later reverted to fam.).