At first, Fanny and Edmund are united in their opposition to the idea of doing such a racy play as Lovers' Vows as a family theatrical. Both are, at first, adamant in their refusal to participate.
However, under the influence of Mary Crawford, Edmund decides to participate. Although he goes to the white attic to speak to Fanny about it, and although he wishes she would approve his lame rationalizations for participating, for the first time they are not seeing eye to eye. Fanny continues to think he should not act. She believes he should remember how his father would disapprove of the venture and stand up for his father's principles. She also is jealous of the idea of his playing opposite Mary.
While Fanny is subjected to censure for her refusal to act, she holds her ground, foreshadowing her refusal later to marry Henry Crawford.