I (24F) have a half-sister (27F), we'll call her Taylor.
My dad had weekend visitation with Taylor at our house until I was 8, and it was the worst. She bullied me really badly any time I saw her, to the point that I would scream every time my dad even mentioned her coming over. Even if we were kept apart, she would break my things, upset my pets, and tell lies about me. Every week her mom would end up in the kitchen screaming at my parents.
Taylor's mom died when she was 11. Her mom didn't have any family able to take her in, and nor did my dad. My dad was the only one who could get custody. When I was told about this, I freaked out. Screaming, crying for hours, calling my grandparents and demanding to live with them, all of it. My mom wasn't willing to have Taylor in the house on that basis, and I'm pretty sure she said she would move out if my dad pushed the issue. Taylor ended up being sent to boarding school the next year, and she would go to stay with other members of my dad's family during breaks. When I was 14 my parents divorced, and I would see Taylor every few months at my dad's during school breaks. I'd learnt to stand up for myself and she'd grown up so there was no bullying, but we'd bicker - she was hostile and I never backed down. I didn't see her much after she went to college, and then I went to college far away as well.
We now live in the same small city (I moved here in March). It's the kind of place where everyone from each generation knows or knows of each other. I had never encountered Taylor socially and never mentioned knowing her, but I had met her boyfriend and his friends are part of my larger social group. The other night, I was at a party, and Taylor and her bf were there as well. We made eye contact and waved, but she pretty much avoided me all night. During the night, our mutual friends asked how I know Taylor, and I said we are half sisters. They all looked super uncomfortable and I pressed for an explanation. Basically, Taylor's been telling everyone that she was homeless as a kid because her stepmother and half-sister hated her and demanded she be shipped off to boarding school and made her dad ignore her. Were it not for the fact that it was obviously going to come out sooner or later that we are related, I probably wouldn't have bothered to set the record straight. As it was, I'm going to be around these people for a long time, and I didn't feel I should have had to walk around burdened by the weight of her lies. So I told the group the context.
She called me yesterday to yell at me. Apparently she's being ostracised from the group, her relationship is in trouble, her career opportunities are in jeopardy, etc. I don't see how any of this is my fault because she's the one who lied, but according to some people I should have been a bit more gentle in my retelling of the facts because it's her 'experience' and I've basically blackballed her.
EDIT - I didn’t have space for this, but just to clarify what I actually said to the friends. I explained that the reason my mom didn’t want Taylor to live with us was because of the bullying, and that when they split my dad still didn’t have Taylor live with him, and that I only stayed with him on weekends (Taylor told them I moved in with my dad so that she couldn’t). I also told them it wasn’t true that I told my dad not to finance Taylor’s business when she was 20…because I didn’t. That was pretty much the gist of it.
Edit 2 (it was suggested I add this from the comments): I know the answer to these.
My mom didn’t say to send her to boarding school. What my mom said was, Taylor is not living in this house with my daughter, if that means we split, then we split. My dad didn’t want to be a full time parent by himself, so he stayed with my mom, and since he didn’t have any other family Taylor could live with for various reasons, he sent her to boarding school.
My dad never cut contact with Taylor. He visited her at school (it was about an hour away) and sometimes he’d see her at other relatives’ places during school breaks. When he moved out, Taylor would occasional spend the day and maybe one break a year at his place.