Each side in a criminal trial gets a number of "preemptive strikes" of potential jurors without needing to show cause, and then may request a strike "for cause," i.e. obvious bias or connections with the defendant. This person was not stricken, and sat through the presentation of the evidence so she may have very good reason to support the prosecutors, unlike the senators who made up their minds to acquit trump before the trial, some announcing to the press in advance, and voting to acquit him after refusing even to review all the evidence and witnesses, in violation of the oath that they took to sit as impartial jurors.
Stone was convicted of witness tampering and making false statements to the House Intelligence Committee, crimes that involve only his own personal conduct. Hart obviously concluded that he was guilty. If the judge's charge to the jury accurately stated the governing law, she and every other juror were free to decide for themselves.
Moreover, in the real world, I would doubt that an entire jury could be impaneled that, to a person, did not have an opinion of trump.
