Mary, in consequence of being the only plain one in the family, worked hard for knowledge and accomplishments, and was always impatient for display. Jane facilitated her sister's desires as much as she could, assisting her in her playing by turning her pages and pointing out her errors in the mildest of tones.
Despite her natural vanity, Mary took a little heed of her eldest sister's manners, and softened her usual pedantic air and conceited manner, enhancing her performance greatly.
After playing a long concerto, Mary was glad to purchase praise and gratitude by the playing of airs for dancing.
Author's note: here we see a remnant of my drafts – Jane taking the place of a mother. In my construction of Pride and Prejudice, Jane and Lizzy try to fill the absence of both father and mother, and since Lydia is not yet out, their efforts are not rebuffed as much as when she does come out. This also partially accounts for the way Jane has not yet retreated into herself, only looking to Lizzy to disclose her thoughts.
Disclaimer: I don't own Pride and Prejudice, novel or films.