I'm not suggesting that being open minded requires giving all ideas equal credence, that's a strawman. Just that us humans tend to have strongly held opinions that are wrong far too often - like your sister in this case. If she was more open minded about her own beliefs that would be beneficial.

I think antivax claims have been given equal credence, they've just been found false.

A better example is that equal time is frequently given to both sides of the climate change debate despite the actually numbers showing that calling it a "debate" is journalistic laziness. Equal credence would mean the deniers only get about 3% of the allotted time to make their crackpot case, because that's the closest they come to being a "side" in this non-debate against the other 93% that also have 100% of the data and research.

It's like spam in a decentralized system. Attackers can't change consensus within the system but they can slow it down to a crawl. Proof of work in Bitcoin is just an anti spam mechanism.

Your sister grew up with you and went through the same schooling as you.

Doesn't she deserve to be heard? By labeling her a antivaxer and ignoring her based on that label you effectively are closing your mind to her.