Tiaral

Also, keep in mind that if you kill her, she might be declared a martyr, and the cult could actually become even stronger...
You need to fight something like that with other means. By the way, I was hoping to dispel the mind control from Aritha with Sirocco, back at the mansion, when we got our gear and skills back. Fight evil words with good words!

Cop, you yourself are writing about mind control. So, it would be strange to declare her a martyr if the mind control fades when she dies. I don't think it can be overcome by other means. Unless with something very rare and exotic. In any case, the cult largely depends on her personality and abilities, so even the martyr option is better than a living Koko. They will have to look for a new leader, which will almost certainly lead to a schism in the organization. It will also have a negative impact on recruitment. And then the cult's opponents will make themselves known.