I've never been quite certain of why Elizabeth dreads telling her mother that she's engaged to Darcy. Of course her parents think she dislikes him---thus her father's extreme concern about her acceptance---but I can hardly imagine her mother being distressed over any respectable engagement whatsoever for any of her daughters, let alone a gentleman worth ten thousand a year. After the way Mrs. Bennet tried to pressure Lizzy into marrying Mr. Collins, she could hardly have turned up her nose at Darcy if her sole concern is to get her daughters married.