I think that there's certainly a nucleus of truth in Mary's belief that she's "neglected". I think that Sir W does not regard her at all. I think that he had some slgiht regard for Anne while she was prettier but Mary is not very pretty, not "his pet" like Eliz and her husband, while a perfectly good match, by most people's standards, was considered "not quite grand enough for an Elliott" by him...so that meant that she was not admired by her father for getting a husband...