I think that Anne is wanted by the Musgroves to the degree that she is useful to them. They do treat her better than her own family, to be sure, but that is not saying much. They take her into their confidence, but they don't really want her advice. They do so because they think she has some influence with Mary and they hope she can be useful there. It never occurs to them that Anne, still unmarried, might occsaionally like a dance, but she is never asked. She is just kept at the piano to play country dances by the hour. Anne's real musical talent is left ignored in favor of singing and harp playing. Anne is never allowed to exhibit in the manner of Musgrove girls. When it comes to minding Mary and Charles' children its almost a given that the task will fall to Anne. She is happy to have something to do, but they definitely take this service for granted. I don't see Henrietta and Louisa taking care of Little Walter & Charles Jr.