This passage from Ch 4 may reveal how Fanny was treated, especially that last sentence. Poor Fanny, with her retiring, shy, and intimidated disposition! To be so set upon that spending her time with Lady Bertram (full-throttle nap attack)should be an utter delight. Can you imagine Emma Woodhouse or Elizabeth Bennet lasting long with the likes of Lady Bertram? (sprouting roots into that sofa)

".....Fanny had no share in the festivities of the season; but she enjoyed being avowedly useful as her aunt’s companion when they called away the rest of the family; and, as Miss Lee had left Mansfield, she naturally became everything to Lady Bertram during the night of a ball or a party. She talked to her, listened to her, read to her; and the tranquillity of such evenings, her perfect security in such a tete–a–tete from any sound of unkindness, was unspeakably welcome to a mind which had seldom known a pause in its alarms or embarrassments....."