I never figured out if she was his wife, or his servant, but she was the woman who came to the door when D'Hubert first sought after Feraud, to deliver the message that he was to be arrested for duelling. What was her character's name, or who was the actress?
She also appears in Kubrick's 'Barry Lyndon', as the manipulative Irish girl over whom Ryan O'Neal's titular character fights his first duel.
Ridley Scott was such an admirer of Kubrick's visual style in 'Barry Lyndon' that he admits to borrowing heavily from it for 'The Duellists' in terms of lighting, framing and pace. He was evidently also happy to cast one of Kubrick's actors, having been impressed by her performance in 'Barry Lyndon'.