Dear Amy I'm surprised you didn't give LW1 the most basic and relevant piece of advice: talk to her sister about this!!!! Communicate directly to her sister her feelings and expectations! How can she expect her sister, who is being ridiculous, and cousin, same, to be mind readers???  Yes it's an unfortunate dynamic and it's not fair it's hurtful.  But setting boundaries does require communication.  And LW's communication via silence for 9 months is clearly not getting her the desired outcome.