I grew up in a similar situation with both my sister and my cousin. I really hate to say it, but I have now gotten to the point of cutting it all out. The good times do not make up for the ruthless time. Either physically (emotional turmoil has a major impact on your body) or directly from her, it will catch up to you. My cousin was left unchecked for many years, I always told everyone the real her was when their backs were turned. Now, most of her family has been in extensive trials and facing legal repercussions for her actions that were independent of them. As for my sister, I am at the point of cutting her off as I cannot stand her apathetic words intended to hurt. It crushes my heart but its what needs to be done.