The victim impact statement isn’t evidence in the trial. The trial has already wrapped up. The impact statement is part of sentencing, when the court is deciding what an acceptable punishment would be. The guilty verdict has already been made, so the rules surrounding things like acceptable evidence are much more lenient.

The reason she wasn’t allowed to make a scene during the trial is because the defense can argue that her outburst is tainting the jury. It’s something the jury is being forced to witness, which hasn’t gone through the proper evidence admission process. So if she makes a scene, the defense can say that the defendant isn’t being given a fair trial because inadmissible evidence was shown to the jury, and move for a mistrial.

It sounds harsh, but the prosecutor told her to be stoic because they wanted the best chance of nailing the guy. If she threw their case out the window by loudly crying in the back of the courtroom, that wouldn’t be justice.