Exceptionally pretty, Lucy ensnares Edward's affection while he is her uncle's pupil. She herself has little education and no money and is glad of this opportunity to come up in the world. When Sir John invites Lucy and her sister Anne to Barton Park, the sisters are shrewd enough to bring presents for the children and to flatter their mother into thinking they dote on them. Thus they soon win her favor.
Lucy is determined to become intimate with the Misses Dashwood, whom she praises as "the most beautiful, elegant and accomplished and agreeable girls." Clever and cunning, Lucy confides her secret to Elinor and watches for her reactions. Knowing that Elinor doubts her story, she shrewdly shows her a letter and picture from Edward. She acts her part well, but Elinor is not deceived, rightly seeing Lucy as "illiterate, artful and selfish."
When Fanny Dashwood and Mrs. Ferrars are pleasant to her, Lucy is delighted. But her sister tells Fanny about Lucy's secret engagement, and Fanny orders her from the house.
Not averse to lying, she declines Edward's offer to release her from her engagement but tells Elinor that it was she who offered to set Edward free. Then she subtly flatters Robert and beguiles him into eloping with her. She insinuates herself into the favor of old Mrs. Ferrars by flattery and false penitence, and actually becomes the old lady's favorite daughter-in-law.