Good insights on the forming of Mary's character. I can easily see her going through all that.

Perhaps another influence on Anne's character was the way that she was downtrodden for so long after her mother's death, so much so that all trace of the Elliot pride is gone. Mary escaped a bit earlier, so she still has a fair share left - and as you say, always being pettish because she never got as much attention from Sir Walter or Lady Russell.

I imagine that Mary has the same type of looks as Sir Walter and Elizabeth, but to a much lesser degree. This, IMO, would explain their behaviour towards her and her resulting character.

] no doubt she discovered on being ill that she received some attention. This was just a step away to realizing she could vie for attention by being 'sick'. Eventually, I would imagine it would become a way of life.

Yes, especially considering her Elliot sense of her own worth. I'm sure it worked very well with Charles too until he got used to it. But poor Mary doesn't seem to realise that he likes and pays more attention to her when she's not feeling ill.