There's a bit in 'The Making of...' on the DVD where the actress who plays Mrs B says that when she read the book, the character was 'just all there' - she'd never read the book before and she loved the way that Mrs B just 'jumped off the page'.

I don't agree with critics that say she is 'two-dimensional' in the book. Mrs B is just a very shallow character in most ways, there isn't much of a third dimension to begin with. LOL!

If she were written as a two-dimensional character, we would be left with the impression that there is more to the character than the print says. With Mrs B, I get the impression that everything there is to say about her character is said right there on the page, I never get the impression that there is any 'hidden depth' to her. And yet she 'feels' like a real person, not a charicature.
The way she's played in P&P2 she comes across as a real person, she's never unbelievable (but invariably silly... LOL!!)