The prelate was a strong beliver in Prophecy, so she instructed all of the Sisters not to tell Richard of the Wizards Web that slows time in the Palace down. Because of the Prophecy that said Richard was doomed to fail in his quest to defeat The Keeper, none of the Sisters were allowed to tell Richard of the Wizards web over the Palace, for fear that he might leave and continue on his quest, and then the prophecy would come true.
Sister Nicci, who truly was a Sister of the Dark, defied the Prelate and told Richard of the Web. Angry, Richard devised a plan to escape from the Palace. Because the headaches he was getting from his Han, Richard agreed to give his to Nicci who could then break down the magical barriers surrounding the Palace. But once she had done so, Sister Verna put a Rada'Han around her neck (part of Richard's plan), rendering all her new power useless and made Nicci a prisoner.
Richard escaped and the Prelate and Verna tortured Nicci to have her reveal to them the other Sisters of the Dark, but they had already fled the Palace and were working to help Nicci escape, which they did. Richard had wandered into the Valley of Perdition. After Richard left the Creator revelaed a new Prophecy: " As long as the Mother Confessor's pure heart beats, the Keeper is doomed to fail." After learning this the Prelate decides to hold Kahlan hostage so she can't be killed.
But with Verna's help Kahlan and the others escape and Richard escapes from the Valley and together they kill Nicci.
The Prelate was the one who had the young woman Maia brought to the Palace, telling her that she was the creator born into a mortal body. So her power could manifest, all of the Sisters surrender their Han to her, making her incredably powerful. It was never proven if Maia was really the Creator or just decieved by the Sisters, the Prelate still wanted Richard dead so the Prophecy couldn't come true.
As the Prelate of the Sisters of the Light, she is no doubt a very powerful sorceress. She has skill in using a Dacra and once she threatened to kill First Wizard Zeddicus Zu'l Zorander with a dacra, had she absorbed his Han with it she would be even more powerful. Despite that she isn't quiet fast enough to cast or counter her spells, as Zedd questioned if she could kill him before he burns her with Wizard's Fire and when Verna stated that she can release the Dacra's power before she can remove it, when she hits her with a dacra. She can also cast powerful barriers which could prevent people from entering or leaving an area, though Nicci manage to break her barrier and replace it with one she cannot break down. Its possible that she gave her Han away to Maia losing her magic.