I was going to share with you, gently, that it seems by all you've shared that your sister and her daughter are quite possibly narcissists. Your sister seems to have taught your niece that it's okay to treat you like this, so she's at the very least a completely self-absorbed young woman; and, at worst, a narcissist like her Mom.

It took me years to piece together the truth of a very similar situation with my own sister and niece. I am still healing from years of game-playing and devaluation of me that my sister engaged in. It does help to become as educated as you can about the disorder---because it affects you profoundly as a sibling, whether you ever realize what it actually is propelled by, or not.

I could write a whole book about what it created, and destroyed, in my life. But I'd rather hug you and tell you, You are NOT alone!

Getting our heads around the disorder helps by removing the continual and soul-scouring self-examination and ruminations, wondering what we could have done differently. Narcs are geniuses at turning it all into OUR problem, OUR shortcomings. Don't take the bait!

I've also learned that any reputation damage my sister tried to inflict over the years fortunately only had short staying power. People pretty much knew me to be a much finer person than the "me" she tried so desperately to portray. So it largely backfired on her. And I'm at an age now where I basically do not give a rat's about what anyone thinks of me, anymore, anyway---even if they were once highly-respected family members.

I hope you know you're not the only person to have suffered these humiliations. You can move on, and you can heal.

It takes time and perspective, but it can happen.