Catherine Vernon (née De Courcy) is a character in Lady Susan. She is the wife of Charles Vernon, brother-in-law of the infamous Lady Susan Vernon. She is the daughter of Sir Reginald and Lady De Courcy and sister to Mr Reginald De Courcy.
While Catherine was engaged to Charles Vernon, head of the wealthy Vernon family and owner of Churchill, a large estate, she made the acquaintance of Lady Susan Vernon, her intended's sister-in-law. Catherine knew that Lady Susan disliked her because of her upcoming marriage to Charles, for whatever reason, but the lady behaved with the gentlest and sweetest decorum. Besides that first meeting, however, Catherine noticed how Lady Susan got rude and ungenerous toward her fiancé during the few months until their wedding. She relayed these observations of the lady's unkindly disposition to her mother.
Catherine and the rest of her living immediate family keep up a steady correspondence, and oftentimes Reginald is very forward with his sister, particularly about his feeling on Lady Susan and calls her a "coquette"—which is usually language that men at the time tended to keep quiet around women (even sisters). Catherine was surprised about how genteel Lady Susan acted when meeting her, even though she knew the grand lady despised her for marrying Charles Vernon. Catherine's heart goes out to Frederica Vernon, Lady Susan's quiet and very bullied daughter, as she does not think Frederica deserves even a quarter of the ire Lady Susan directs at her.
Catherine allies herself with Frederica, her niece, and is annoyed that her brother parrots Lady Susan's negative words about Frederica. Catherine complains about her brother and Lady Susan to her mother over several letters. She takes it into her head that she must make Reginald sensible to what is happening between Lady Susan and her daughter, and notes in letters to her mother that Frederica has become a favorite among Catherine's own children.