She was married in 1222, which argues for a birth date c. 1200 - c. 1210 (possibly a little earlier, but no later).
If those *are* her parents (which is somewhat open to question, as she is consistently described as the "niece of Walter (de Grey), Archbishop of York"), their birth dates need moving back an absolute minimum of ten years.
Walter de Gray/Grey, Archbishop of York, was probably born between c. 1175-1184. His parentage is somewhat disputed, but it is clear that he was the nephew of an earlier John de Gray, Bishop of Norwich and might-have-been Archbishop of Canterbury (King John wanted him, and actually got him elected, but the Pope set aside the results and installed his own candidate, Stephen Langton). He had an older(?) brother named Robert, on whom he bestowed various lands, and a sister Hawise, who is said to have married the Justiciar Philip Basset (c. 1185 – 19 October 1271).