Orual (agent)

You could be looking for the canon character from Till We Have Faces.

Agent Orual is an Assassin in the Harry Potter division, who works with Agent Gus McFerrin. She is best known for, with Gus, stumbling across the secret of Pink and Purple Stuffs on a mission.

Origin
She was originally recruited from a Chronicles of Narnia badfic, where she had been a hag who the Gary Stu and the Pevensies were to fight.