Good going by putting your foot down. Just because you're twins doesn't mean she is above the rules or can abuse you. I have a twin sister as well and we were raised not to argue or express dissatisfaction with each other, share everything, you probably know the drill, lol. The fact is, twins need boundaries too. Continue to lay down the law. Other people in your family won't like it because life is easier when everybody can sit down, shut up and don't cause them any problems by upsetting that once person. Accept that they won't like it that yore out of their self imposed Matrix. Stand strong and continue making the most out of life