This question has always intrigued me also! In addition to the “perhaps he thinks it gloomy” line already cited, there is her reaction to the news that Rochester is going to marry Jane – is she really concerned about their differences in age and status, or is Bronte trying to create a little mystery here?
And what does Mrs. Fairfax think Mrs. Poole does up there every day, all the time? I think Rochester tells Jane that only Mrs. Poole and Dr. Carter know about Bertha. Jane describes Mrs. Fairfax as being of average intelligence and not curious – she doesn’t know how to describe Mr. Rochester to Jane very well – and she seems to buy into the idea that gentry are our superiors and are Not to Be Questioned. While at least one of the movie or TV versions (I’m thinking of the TV version with Samantha Morton as Jane and Gemma Jones as Mrs. Fairfax) goes out of the way to make sure to establish that Mrs. F thought that it was Adele’s mother in the attic, I’ve always thought that Mr. Rochester just told her, “I’ve given Grace Poole a special job to do. She’ll be spending nearly all of her time up in the attic from now on, and you are not to interfere,” and that was good enough for her. Yeah, weak I know.
Re Rochester’s thoughts on Adele’s parentage – I think once he got burned by Celine’s cheating on him, he figured there’s no way to know how many men she may have been fooling around with, so in a time before DNA testing, how’s he supposed to know he’s the father? But on the off-chance that he is the father, or in any case to keep the poor kid from being raised in poverty and even danger, and because he wants to show God how hard he is trying to be a better man, he has her provided for in France for a few years before bringing her to Thornfield. He certainly doesn’t act like he thinks of her as his own daughter, though.
You simply must get your hands on the 2006 Masterpiece Theatre version with Toby Stephens as Rochester. He’s great, although personally I still think Timothy Dalton is the champ. Of course I am looking forward to seeing Michael Fassbender in the role (if it comes here – I may have to wait for the DVD. Arghhh!).