Until that point, Estellise did not pose a problem. So likely, yes, it was her powers. However, unless removed from Alexei in some way, his use of her and her powers would continue to cause problems. Simplest solution, remove Estellise. Although I would have likely tried to gut Alexei himself, for the Entelexeia he killed.

[ Oops there is clearly more irritation at Alexei than anything he felt for needing to remove Estelle.

Duke doesn't seem sure why he chose that particular word. Oh well. ]