This struck me as well...

If someone was to hand this book to someone saying that it is a very good read, and the receiptiant was to ask what it was about...and the answer was that it is of a woman who was disappointed by a gentleman year's before...would you not think that this book was about Elizabeth?

She had had a disappointment, moreover, which that book, and especially the history of her own family, must ever present the remembrance of. The heir-presumptive, the very William Walter Elliot, Esq. whose rights had been so generously supported by her father, had disappointed her."

We are told so much more of her than any other character save Sir Walter and Mrs. Russell.

She is selfish, vain, and bored.

Hmmm...maybe this is a story of growth? From their financial straights, maybe she improves in character?

But it's not until the last sentence in chapter 3 that it actually hits the reader that Anne is the heroine. Oh and what a sentence it is:

Mr. Shepherd was completely empowered to act; and no sooner had such an end been reached, than Anne, who had been a most attentive listener to the whole, left the room, to seek the comfort of cool air for her flushed cheeks; and as she walked along a favourite grove, said, with a gentle sigh, "a few months more, and he, perhaps, may be walking here."