I find myself trying to be fair with her. She´s such a very secondary character and our heroines don´t pay her much attention (and the adaptations too) that it´s easy to forget her.
I don´t find her faulty or disagreeable, at least for now. I think they don´t have much in common, that is, the Dashwood are very interested in the arts, and the improvement of their minds ;) and Lady M not. But she offers what she has. In real life it´s a common situation, to be together with people with different interests. Learning to appreciate them and doing it sincerely is something worth doing. So I´ll pay attention to how this relationship evolves.
Perhaps it was Jane who found people like Lady M insipid. By then she was young and perhaps more prone to judge harshly what she didn´t like or share.