That is a speculation about Lady Anne but it seems to be a matter of going on what is not there i.e lack of documents rather than what is. To me, there's simply no evidence to suggest Lady A thought the match an excellent idea, we only have Lady C's word on it. I don't think the fact Wickham knew of engagement rumours necessarily affirms them- he may've simply heard Lady Catherine talking when she visited Pemberley. Actually, I have the impression that by Ch.58 when Lizzy accepts Darcy, he has learnt humility in helping the Bennet family while Lizzy has learned forgiveness of Darcy's past over-bearing pride and prejudice against her middle class background. With P&P, Austen criticizes the class structure of Regency England. With the charecter of Lady Catherine JA presents a satire of the upper class,showing a woman more concerned with superficial morals, social hierarchy, enforcing social etiquette rather than setting an example virtue or real manners. By the way, I didn't mean to say Anne would make Darcy the ideal wife. I meant those reasons of keeping the esates within the family and maternal nobility were excellent reasons in the mind of Lady Catherine, particularly as she had no son.