Mrs. Smith’s common name belies her uncommon character. Faced with a truly astounding run of bad luck (husband dead, money gone, health gone, friends walking out), she still manages to stay cheerful. Anne decides that it’s simply Mrs. Smith’s nature to be happy: "here was that elasticity of mind, that disposition to be comforted, that power of turning readily from evil to good, and of finding employment which carried her out of herself, which was from nature alone" (17.7) – unfortunately she can’t make her fortune from bottling and selling Mrs. Smith’s Happy Juice. Mrs. Smith shows that happiness isn’t always dependent on what you have – sometimes just who you are is enough.
What Mrs. Smith does have, however, is information and experience. While Anne is disposed to think the best of people, unless she’s given reason not to, Mrs. Smith knows how bad people can be. And it’s her previous experience of being burned by Mr. Elliot that enables her to keep Anne from suffering the same fate.
Mrs. Smith doesn’t share her information on Mr. Elliot, however, until it almost doesn’t matter any more. She believes that Anne is actually going to marry Mr. Elliot, so she keeps her mouth shut. However, once she’s convinced that Anne’s not interested in the man, Mrs. Smith spills what she knows about his past sins.
Why doesn’t she tell Anne the dirt on Mr. Elliot when she first hears of her friend’s involvement with him? Mrs. Smith herself gives a few reasons: she thought it wouldn’t make any difference in a marriage already decided, she was trying to respect Anne’s supposed engagement by not badmouthing her husband-to-be, and she thought Mr. Elliot would treat Anne better than he treated his first wife. Perhaps some or all of these reasons are true, though it’s also possible that Mrs. Smith was hoping that she could get at Mr. Elliot through Anne and force him to restore her lost fortune. Eventually, however, she puts her friendship first, and still ends up getting her fortune back through Anne’s husband – Captain Wentworth.