I think Lady Russell and Anne are mutually the most important people in each other's lives at this point. Childless Lady R has become the Mother figure to Anne who is a cherished surrogate daughter and as such, is her nurturer, defender, and protector. It is a testament to Lady R's good breeding and manners that she does not directly chastise Anne's blood relations on how they treat her disrespectfully and indifferently.

From the author, we already know a lot about Lady Russel in that she does not have the penetrating insight and understanding of Anne but has always acted honorably and in what she considers Anne's best interests.