He [William de Warenne] married, 1stly, Maud (m). [Complete Peerage XII/1:500-03, (transcribed by Dave Utzinger)]
(m) She is alleged to have been daughter of an Earl of Arundel, to have d. 6 Feb 1215/6 and to have been buried in the chapter-house of Lewes Priory. The date 6 Feb. (no year) as the date of death of a Maud, Countess de Warenne, is confirmed by an Obit in the Beauchief Abbey Register.
Note: Based on the above, I have placed her as daughter of William d'Aubigny, Earl of Arundel during the right time frame for Maud.