Co-founder with her husband of Lewes priory, 1077. Her tombstome placed in St. John's Church, Sonthover, Lewes, at end of eighteenth century (The concise dictionary of national biography. Part 1 : from the beginnings till 1900. London : Oxford University Press, 1969, pg. 544). aka Gundreda (Browning, Charles H. Americans of royal descent, 7th ed. Baltimore : Genealogical Pub. Co., 1986, pg. 389). aka Gundred (Browning, pg. 442). It has been suggested that she was the illegitimate daughter of Matilda and a Flemish commoner named Gherbod (the relationship perhaps also producing a son named Gherbod, who later received the Earldom of Chester). The point is in debate - Browning suggests she was William's daughter, but most other texts I have consulted do not include her among his children (Williamson, David. Debrett's kings and queens of Britain. Topsfield, Mass. : Salem House Publishers, 1986, pg. 46).
The entire topic of William's daughters is in question. The list of them varies form one source to another. By and large Grundrada is omitted from them, with the exception of Browning and a source found on the Internet. It was posted on soc. genealogy.medieval on 4/10/1966:
"I copied a few pages from a book I found called "The Warren family." It is large and covers many English lines in detail. From it the following appears:
" Sir George Duckett, Bart., who has made a special study of the Charters of Lewes, had produced evidence to the fact the Gundreda is described as Matilda's daughter, and the queen does not seem to have had a husband previous to William the Conqueror to whom she came as a young unmarried girl. Among the benefactors of Lewes Priory, Matilda is described as the mother of King Henry and the Countess Gundreda, while in the Charter of William I of the Manor of Walton in Norfolk to Lewes Priory he calls Gundreda his daughter (filiae Meae)... again in the Ledger Book of Lewes, speaking of William de Warrenne, it is said he married the Conqueror's daughter ('cujus filiam desponsavit')."
It would appear that William I contracted a marriage with Matilda about 1049 without Papal sanction, and that the Council of Rhiems prohibited the marriage; which had in point of fact taken place. The children born would thus be placed in a dubious position. The next Pope confirmed the marriage, and the children born after this had the right of succession to the throne of England; but not the former issue. This, however, did not affect the paternity of Gundreda more than it did that of her brothers Robert and Richard; so that we are disposed to accept the conclusion of Sir H. Ellis in his introduction to Domesday Book, that "Gundreda was really daughter of the Conqueror."
The issue was addressed by David C. Douglas in his definitive biography "William the Conqueror : the Norman impact upon England" with the opposite conclusion: "At one time it was held that when William sought her hand, Matilda was already the wife of a certain Gerbod, by whom she had a daughter, Gundrada, who later became the wife of William of Warenne, the first earl of Surrey. This, however, has now been finally disproved, and it is in the highest degree improbable that Matilda was married to anyone before the Conqueror (pg. 76-77). The view once held that Matilda was already married when William sought her hand, and was then the mother of a daughter, Gundrada, later the wife of William of Warenne, has now been conclusively disproved by the researches of Chester Waters and Sir Charles Clay. There is no reason to suppose that Gundrada was the daughter either of William or Matilda (pg. 391).
Despite Douglas' opinion the primary sources cited above would seem to indicate that Gundrada was indeed the daughter of William.