Looking at the Wikipedia article, I see that they are associating her with a comedy of manners, which is similar but not the same as the novel of manners. I would say that the canonical novel of manners is Pride and Prejudice, which while often funny is not a comedy at all. A canonical comedy of manners might be An Ideal Husband. The difference is that the novel of manners is realistic in tone, while the comedy of manners is absurd and formalistic. I personally prefer the novel of manners, though I also like the comedies.

I personally don’t think Willis is a particularly good example of the comedy of manners, either. I think her best works are the ones which are least funny.