You know, at this point I agree with @Timo. She was resentful of the whole Stargazer fiasco. Picard was later absolved of all charges, but she made a fool of herself because she was being too hard on him when it was evident that he was not at fault and it should have been just a formality.Essentially the trial disproved and proved nothing.
Riker "proved" that Data was a machine, which was never really in dispute.
Picard "proved" that Data could be self-aware but that we have no way of proving it one way or the other.
We're back where we came from.
She agreed with Maddox only to spite Picard. But during the hearing she realized that her name would forever be linked to the one who created a race of slaves.
She then she tried to limit the damage and she made a speech that was meant to be noble and inspired but that in reality made no sense ("We've all been dancing around the basic issue: does Data have a soul?": WHAT THE HECK ARE YOU TALKING ABOUT!?).