I think i got the same bug as you. In my last run. I KO'd her at the Grove defense. I entered her mind and told her to fight with me. After you killed the 2 gnomes torturers you can't talk to her. Nothing. So i loaded an old safe file and attacked the gnomes directly. And it worked then. But i got the Cerys bug in the gnomes fight. Cerys turn was always only a Black screen. And after the gnomes fight this Cerys bug was gone.
At first i KO'd her at the Goblin Camp. The scene with Ketherick at Moonrise was played as normal. But after that Minthara is standing like a Statue in the throne room. She was not teleported to the torture chamber. You can't talk to her. It was completely impossible to recruit her.
