It's just that a pretty girl like Wyrene had to undergo a harsh interrogation to get the names of Trisha and the other conspirators from her.
And in this case water torture would have been ideal, for it would not have damaged Wyrene's appearance, forcing her to endure great agony. Also, the sight of Wyrene lying on the torture table, with her swollen belly from swallowing water and the executioners pouring fresh water into the funnel in the girl's mouth and groping the girl's bulging belly with care, would have been very inspiring and revealing of these harsh times.