If she is charged, then she can question each of the purported voters under oath and ask if those are their signatures and also subpoena copies of other documents with their signatures to compare. She didn’t “reproduce a voter’s signature” if those were not the voters’ signatures.
She showed that the voter signature on ballots didn’t match the voter signature on file. Her tweets showed the voter’s typed name on a form that was on file, the voter signature on file, and the signature on a ballot. They did not match. However, she did reproduce the actual voter’s signature on file with the election’s office, so she may be in trouble there.