Burke names her as Sybilla in one work and Matilda in another!
After her husband drowned she became a Nun, and was elected abbess of Fontevrault.

When the white ship was wrecked on the deadly rock a boat was launced and William, the Kings only legitimate son, was rowed to safety. The cries of his half-sister the Countess of Perche induced him to return to the wreck where they sank together. This was considered by some to be punishment for Henry's sins of lust in having so many illegitimate offspring.