What a challenging situation. You are being there for your niece just by trying to muddle through this emotional quagmire. Share what you remember, but also share how challenging it all is. I'm sure she is also having a lot of challenges around the subject and it can be something you relate to each other over. I have some problematic people in my family too and what has helped me is thinking of Sir Thomas Malory, certified very bad dude, who wrote Le Morte d'Athur while in prison. That works became the cornerstone for Arthurian legend which I love so much and gained so much inspiration from. Without that certified bad dude, there would not be those beautiful stories I love. People are really complicated and where there is great darkness there is often great light as well. That is the beautiful thing about being human, we are none of us two dimensional. I am sending love and light and I hope this experience helps you both get closer to peace.