I agree with your analysis. Lady Russel knew that FW did not choose to renew his engagement after he had made a fortune. Even when he was thrown in Anne's society again, he rather choose to go after a Louisa Musgrove instead. Her "angry pleasure" and "pleased contempt" at FW seeking after Louisa when he is re-introduced into Anne's society does suggest that she may have had feelings of insecurity about her decision, and was glad to see it "proved" right.