my aunt has made a choice to keep her husband in her life and has allowed him to move back in. I don't understand her choice at all, and have decided that if I can not trust her to keep someone she KNOWS has hurt someone else in that way out of her life,
Abuser abuses the niece. That the family knows. Has the family investigated if the abuser was also abusing the aunt? Maybe he was doing separation abuse to her?
Sometimes abused people have to make that kind of choice -- because the abuser has a hold on finances, blackmail, threatening to kill the children, the victim, god knows!
Maybe she isn't crazy about it but takes him back so he doesn't kill her, the niece or other relatives!
So rather than dump more stuff at the aunt so YOU can feel better (unload all your bewildered at her) I guess I'd keep you bewildered to yourself for a bit and reach out (if you are going to reach out) to ask if SHE is ok first? In need of aid? Help? And ask why she would take back the Molester Uncle? Is she in danger? Can you help her find aid?
And go into it knowing she may not be free to speak/type freely if he's in the room listening and monitoring her/reading over her shoulder.
The leaving time is always the scary time -- abusers are whackadoodle.