That you have love and kindness to share. That no matter what, you can give and receive nurturing energy. When the anxiety and doubt comes, don't fight it. Take some breaths and sit in the feeling. Let the episode subside, then do something nice for yourself.

You have a right to your anxiety and doubt, but your love and kindness is stronger and healing.

...with this unanswerable question.

And please remind yourself of all the good GREAT things about yourself that have nothing to do with anyone other than the wonderful person that YOU are (that might sound silly but you know those great things are there).

Thankfully, I have no memories

As horrible as it is to contemplate as even a remote possibility-- given what you said about your sister-- I'd have to share your doubts that it is anything other than your sister's created delusion. What possible good could come from relating such a story to you or anyone else--especially given you would never have remembered it as an infant? You say your sister is abusive and has many issues of her own. I'd be hard-pressed not to think this story that can only cause pain is likely part of that situation--that instability-- with her. I wish she'd not told you that. I hope you can put it aside and not let it cause lingering harm from something you can (and could) never know. Now that you are an adult, I tend to think the friends/family who discount this story would have little motivation to tell you anything but the truth.

if you have no memory of it or any issues that would indicate such behavior occurred, my suggestion, as a layperson, is to live your best life and leave the toxicity behind. Best of luck

Blessedly, I have no memories. My sister may have god knows what reason to throw that out in the middle of a conversation

It sounds to me as if she wanted to hurt you and I would not give any credence to what she says. You are strong, don't let her "story" eff with your mind.

Of a conversation. Out of the blue. She was very close to him. Thank you