I have changed my opinion of her during this read. I had always liked her before, but had, as stated in another post, thought of her as one of JA's 'caricatures' and not a real 'character' and I'd changed my mind.
What makes her complex to me is the issue of gossip. Marianne misjudges her interest in her sorrow as Mrs. Jennings only wanting fodder for gossip, and we know that's not true. But her gossip does some harm and could make people misjudge her, as Marianne does. I think JA is making important points in this novel about talk, whose stories you can trust and whose you can't, as many posters have remarked on, and this issue of Mrs. J. and gossip is important. If we are well-meaning, 'busy', kind people, it would be even better if we would learn not to say everything we think about people's situations and issues, or we could do real harm, or be misunderstood.