In Chapter 3, it seems as if, in the presence of her family, she is pretty silent, and when moved enough to speak, even hesitates before doing so. (An exception is her eloquent praise of the Navy.) I think no one's given enough affection and attention to her in Kellynch Hall, she must have accepted that her word carries little weight and is barely listened to. Take the pregnant pauses she takes before actually speaking.

"And who is Admiral Croft?" was Sir Walter's cold suspicious inquiry.

Mr. Shepherd answered for his being of a gentleman's family, and mentioned a place; and Anne, after the little pause which followed, added --

"He is rear admiral of the white. He was in the Trafalgar action, and has been in the East Indies since; he has been stationed there, I believe, several years."

...

[Mr. Shepherd says,] "Bless me! how very odd! I shall forget my own name soon, I suppose. A name that I am so very well acquainted with; knew the gentleman so well by sight; seen him a hundred times..."

After waiting another moment --

"You mean Mr. Wentworth, I suppose?" said Anne.

I think that her pauses partly relate to her being silent and insignificant in the family--as if she is making sure that she will not interrupt more important things that Sir Walter or Elizabeth might say.