I'll be completely honest--I feel sorry for Fanny, and perhaps JA wanted her readers to develop a strong sense of sympathy for her heroine. It may be key, as the novel progresses, to be predisposed to feel a sense of kindness towards Fanny.

Or perhaps Austen just wanted to contrast her even more against the character of Mary. Mary is in the same position as Fanny with respect to a home--dependent on the hospitality of a relation. Yet, no one could possibly feel any sense of pity for the spirited Mary. The difference is money--Mary possesses twenty thousand and Fanny nothing. Fanny recognizes her position and is humble. Mary too recognizes her "homelessness" but is unaffected because of the confidence money gives her.