It may be true that Anne is often not heard (and she did not raise her voice!),but as I've written in an earlier post in another thread below, while there may be some similarity between her and Fanny, there are also contrasts between them.

Lady R did not actually overrule Anne, but Anne did not overrule Lady R either! I believe the plan submitted to Sir W was the result of the consultation between them -- re chap 2 --
"She ]Lady R] consulted, and in a degree was influenced by her [Anne], in marking out the scheme of retrenchment which was at last submitted to Sir Walter."

At Uppercross, Anne was so much in everyone's confidence because -- chap 6 --
"Known to have some influence with her sister, she was continually requested, or at least receiving hints to exert it, beyond what was practicable."