How did Mrs. Van Hooper trap Maxim de Winter in a conversation?

The narrator, the unnamed second Mrs. de Winter, is recalling that fateful day years ago when she was first introduced to Maxim. At the time, she was staying at the Hotel d’Azur in Monte Carlo while working as Mrs. Van Hopper's companion and general dogsbody. Mrs. Van Hopper has a reputation of being a real busybody, forever sticking her nose in where it's not wanted. She's also a crashing snob and wants to show off her friendship—in her mind, at any rate—with the suave, debonair Maxim de Winter. She cunningly buttonholes Maxim by approaching him as he walks into the restaurant, saying that as he's a friend of her nephew, Billy, he really must see his honeymoon photos.
Mrs. Van Hopper dispatches the narrator to go and fetch her a letter from Billy. When she returns to the hotel lounge, the narrator sees Maxim and her mistress engaged in conversation on the sofa. Mrs. Van Hopper casually mentions that she and Maxim will have coffee later. Once again, Mrs. Van Hopper is showing off how incredibly well-connected she is, emphasizing the huge gulf in social status between her and the narrator. At this point in the story, she's quite enamored of Maxim de Winter, but her attitude towards him changes dramatically later on, so much so that she actively discourages the narrator from pursuing a relationship with the mysterious master of Manderley.