Barrett wrote her own opinion. Second to last page in the Decision.
She concurred with the majority concerning the Trump case.
However, she rejected the majority consensus which stated that all law and enforcement relative to the Amendment is held by the federal government.
The Electors, who vote in the actual Presidential Election, are chosen in each State by whatever means each State's Legislature decides. The elections you and I vote in are State elections. We aren't voting for President and Vice President, we are voting for a slate of Electors.