She was heir of Beaudesert. (It appears that Beldesert and Beaudeser are the same see below paragraph)

--------------------

Geoffrey Murdac had a daughter, Juliana, who married Thurstan de Montfort, to whom she brought Great Ayton and other lands in Yorkshire in dower, so that in 1166 Thurstan held 3¾ kinght's fees of Roger de Mowbray [Red Bk., 420], besides what he held of Robert de Meinil II.. Thurstan had issue, Robert and Henry, the last named being a father of another Thurstan. In Michaelmis term, 1209(?), this Thurstan demanded a moiety of the town of Langton (E.R.) against Eustace de Vescy as his right and inheritance, taking vestures thereof to the vaule of 100s. and more, to Juliana his daughter, who held that land as her reasonable share which belonged to her, and from Juliana to Robert her son, and from Robert to Henry, brother of the said Robert and father of the said Thurstan, and from him to Thurstan [R. de Fin., 346].
~Early Yorkshire Charters, Vol. II, p. 358

The antiquities of Warwickshire illustrated from records, leiger-books, manuscripts, charters, evidences, tombes, and armes : beautified with maps, prospects and portraictures Dugdale, William, Sir, 1605-1686.

Beldesert. ON the East side of the last mentioned brook, runneth a Hilly tract, bordered with deep Vallies on each part, the point whereof maketh a kind of Promontorie, whose ascent being somewhat steep, gave occasion of the fortifying there, at first, considering its situation in these wood-land parts, where through the oportunity of so much shelter, advantage was most like to be taken by the disherited English, and their ofspring, to make head, for their redemption from the Nor∣man yoak. 'Tis not unlike but that this mounta∣nous ground may be it which we find by the name of Donnele in the Conqueror's Survey; for, as that is therein recorded to be •n the Earl of Mel∣lent's possession, and ranked next unto Preston (before spoken of) so doth the name argue no lesse, don and dune in our old English sign•fying a Hill: But if it were so, this now called Beldesert is of a larger extent than that could be; for that was then certified d but at one hide, having a kind of Parke, or inclosure containing halfe a mile in length and as much in breadth; all which was valued at xxx s. having been the inheritance of Alwoldus in Edw. the Confessors days: Therefore, in case it were so, it must be concluded that a great part of the before specified Preston was afterwards added to it.

From this Earl of Mellent most sure it is, that the greatest part of what he possest in these parts, came soon after to Henry de Newburgh, his Brother, the first Earl of Warwick of the Nor∣man line; who thereof, and of divers other fair Lordships enfeoft eThurstane de Montfort, his neere kinsman. Which Thurstane, finding it so capable of Fortification, erected thereupon that strong Castle, whereunto, by reason of its pleasant situation, the French name Beldesert) was given; which continued; the chief Seat of his Descendants for divers ages; but at length, through coheirs, coming to such Families whose principall mansions were in other places; to pre∣vent the advantage, which in the times of ci∣vill dissention betwixt the Houses of Yorke and Lancaster might have been taken on either side to the prejudice of its owners (as I conceive) was either demolished, or suffred to go to ruine; so that now there is not only any one stone visibly left upon another, but the very Trenches them∣selves, notwithstanding their great depth and wide∣nesse, are so filled up, as that the Plough hath sun∣dry times made furrows in every part of them, to the great advantage of the industrious Husbandman, whose pains, through the ranknesse of the soil, hath been richly rewarded with many a plentifull crop. But of this Thurstane, and his posterity residing here, I will now speak historically.

(Janet Milburn writes: It appears that Beldesert and Beaudesert are the same, strange and quite confusing) 11/21/20 Juliane Murdac is my 26th great grandmother.