[1][2] Isabel was the great-granddaughter of the first Norman earl, William, and his Flemish wife Gundred.

[2] When her father died in the Holy Land in January 1148 she inherited the earldom of Surrey and was married in around 1153 to William of Blois, the younger son of King Stephen, who became earl in her right.

[1][2] The marriage occurred at a critical moment in The Anarchy as part of King Stephen's attempt to control the de Warenne lands.The couple did not have any children and William died in 1159.

[1] William FitzEmpress, younger brother of King Henry II, sought Isabel's hand in 1162 or 1163, but Thomas Becket refused a dispensation from affinity on the grounds of consanguinity.

In April 1164, she married Hamelin of Anjou, a natural half-brother of King Henry, who became jure uxoris Earl of Surrey.