Ser Cauthrien is a knight and Teyrn Loghain's most trusted lieutenant.
Cauthrien may be voiced by Katie Semine.[1]
Background
As a youth she helped Loghain in a fight against bandits, not realising who he was. Loghain was so impressed with her actions, he took her into his service.
Involvement
Towards the end of the game in Denerim, after The Warden rescues Anora, she confronts the party. The player character can either surrender or attack. If you are successful in fighting her, The Summer Sword is gained. If you surrender, you will be taken to Fort Drakon as a prisoner. If this happens, she is met again at the Landsmeet. It appears she wishes to fight you to stop you from interfering with Loghain. However, it is possible to persuade her to let you by without a fight. It seems even she has seen the corruption of Loghain.
Strategy
Cauthrien is one of the more difficult bosses in the game. If possible, try to retreat to a nearby room, so she can be fought without the intererfence of her armed guards.