One morning I was working. I sat in my Pyjamas. My thoughts wandered, and I thought of the sunny beaches of Brittany and the freshness of the sea. By my side was the empty bowl in which the concierge had brought me my cafe au lait and the fragment of croissant which I had not had appetite enough to eat. I heard the concierge in the next room emptying my bath. There was a tinkle at my bell, and I left her to open the door. In a moment I heard Stroeve's voice asking if I was in. Without moving, I shouted to him to come. He entered the room quickly, and came up to the table at which I sat.
Could you help me understand this.
I left her. - Whom did I leave? The concierge? But she was in the next room.
I left her to open. - Does it mean that I myself went to open the door? As if not, because I shouted to him from where I was sitting.
It means that he stayed where he was, and she was left to answer the door. In this context, "left" = to allow someone to make a choice or decision about something, or to make someone responsible for something: I left it up to him to decide if he would come or not.