Thank you. That explains it. I forgot that the boys weren't at home as much.

Yes I suppose she's a brown-noser. I do think that Mrs. Norris would never jeopardize her standing in the Bertram household. However, she seems to have measured up Sir Thomas and figured out how to insert her control over what goes on in their home. It's made easier by the fact that Lady Bertram doesn't seem to have an interest in taking charge other than making Sir Thomas happy. Mrs. Norris seems to have a great deal of influence, just by the fact of getting Fanny there, though she did misrepresent her plans. But even that shows a boldness, to get Fanny there and then say she didn't intend to take her in to her own home.

So does she take an interest in the girls purely for sucking up, or because it pleases her to be taking charge of them, or because of a real affection? She's such a meanie, it's hard to imagine her having affection for anyone. Maybe she takes some pride in that she is their guide and when they reflect back her opinions she likes them the better for it.

I agree with you that it's a bit outrageous for everyone to think Fanny is stupid. She's just a young girl. Why should any little kid be written off like that? It's kind of a bizarre family dynamic. Sir Thomas is stand-offish, Lady Bertram isn't interested, and Mrs. Norris seems only interested in impressing upon Fanny that her place is at the bottom.

It's interesting that it says
Her feelings were very acute, and too little understood to be properly attended to. Nobody meant to be unkind, but nobody put themselves out of their way to secure her comfort.