Everyone breaks laws every day. It's unavoidable. The fact that what she did is "wrong" is unimportant. Toss her from the trial, perhaps. But anything else is a waste of time.
And in reference to your analogy, I don't get your point. Are you saying that if I kill someone and bury the body and *don't* say anything that it's better? No, you'll say, it's better that you don't kill someone, and you're right. But the woman on the jury already committed the "crime" of making her decision before the defense presentation. It's *way* better for everyone that she made this known than if she'd kept it hidden. In this case she is not being punished for making her decision early, she's being punished for letting it be known that she did so.. And that's stupid, since everyone benefits from that knowledge.