The wife of Sir Pitt's brother, Reverend Bute Crawley, Mrs. Bute is a scheming and generally angry woman. She gets very close to the Crawley fortune, but because of her extremely controlling and aggressive ways, she loses Miss Crawley's favor.
In a way we can feel some pity for poor Mrs. Bute. She is saddled with an idiotic husband, no money, and a whole bunch of ugly daughters whom no one wants to marry. In another way, we disparage her for the degree of animus she feels toward almost anyone who interferes with her many plans for getting hold of Miss Crawley's money. Mostly, though, she exists to advance the plot. She makes sure Rawdon is jealous enough of his father to marry Becky and that Miss Crawley is furious enough about this marriage to never forgive her nephew.