Quoted for truth.
I too immediately assumed, upon reading the thread title, that there was sexual abuse involved. I legally emancipated when I was 17 and everybody in my family thought I had lost my freakin’ mind, despite the fact that they all knew my mother was mentally ill. You would think that when word got out that my adopted father was sexually abusing me (word got out against my will - long story), they would be all too happy to recognize that I really needed to get out of that household. But no. It was ‘‘You should have known better’’ and ‘‘This is all your fault’’ and ‘‘Why are you being so selfish?’’ and ‘‘You must be crazy.’’ In fact, my mother tried to get me declared mentally incompetent, and I was so confused at that point that I was willing to let her do this - thank god my therapist put her foot down.
The next six years (six years) were spent trying to keep my distance from this man, who was married to my mother, trying to keep my boundaries when everybody was telling me I should move along, forgive and forget. My mother so desperate to ‘‘just be a family again.’’ When my mother had a different perspective every day - ‘‘Why don’t we just have him take a lie detector test, then we’ll know for sure.’’ Finally, I had to cut myself off from my mother. I was a barely functional mess and it was my last-ditch attempt to find some happiness. It totally worked. I got better. A year later, she divorced him and sent me a card asking for us to have a relationship again. And I agreed. And while she still has some serious issues, our relationship is much more one between equals, and she respects my boundaries in a way she never did.
Losing someone you thought you could trust (my Dad) is hard enough - it’s a million times harder when everybody is bending over backward to rationalize and minimize your pain. I have no doubt, OP, that your sister has been through hell, but you seem completely oblivious to the reality of your niece’s situation. Sometimes things get so thick and heavy that you can’t deal with anybody else’s drama - and while your sister may be a lovely person, there is no question that she’s got some serious drama of her own going on.
And it’s easy - so easy - to feel betrayed in a situation of abuse. I am incredibly close to my own Aunt - she took me into her home when I emancipated, she is the first family member I told, and she supported me 100% - but I STILL feel a sense of betrayal I cannot reconcile with, because she was there the entire time I was growing up. She had no idea about my adopted Dad but she knew my Mom was nuts, and everybody in my family is so terrified of my mother they refused to stand up to her. Even though she is my best friend, and I talk to her every weekend, and I love her to pieces, sometimes I think about those years I suffered and it just hurts. (I would never tell her this - she did everything she could - my point is not to minimize her support but to explain that even though she did everything possible, it still didn’t feel like enough, because abuse fucking sucks.)
Before you can even begin to help your niece, you need to open your mind to the possibility that your family isn’t as wonderful as you think. Your niece is a grown woman, she has a right to do what she needs to do to sort through all of this. If she ever comes to you, and she feels betrayed, you need to hold it. If she feels angry with your sister, you need to hold it. I get a strong sense from your OP that you’re not willing to hold any of that right now, you just want to smooth things over and make them right. Some things are never made right.