I wonder if the judge actually had the power to keep her on jury duty indefinitely. (Contempt of court would be a different matter.) I was sworn in on a jury in L.A. where the defendant took a plea before the trial concluded. The judge made a speech thanking us for our service and saying the good thing was we had served our "one trial" and could now go home. (This was when service was two weeks or one trial.)
We happily returned to the jury waiting area where we were informed that a judge does not have the power to interfere with the jury-selection process, and that, because we had not gotten to the point of deliberations, the trial didn't count and we would have to continue to serve until our two weeks were up. (I won't describe the screaming and cursing that ensued.)
Of course, the law may be different in New York. Or maybe somebody quietly pointed out to the judge that he could jail the juror for contempt, but he didn't actually have the power to keep her on jury duty forever. So he made a show of letting her go.