I need help with the Dark Urge route in act 2, specifically with Isobel.

There is a moment, when the butler Sceleritas Fel tells me to kill her. I go to her to tell her that I am NOT going to kill her. In this moment, all ok.

After talking to her, the mission doesn't appear as done. Therefore, I don't get the following cinematic when Sceleritas Fel tells me to kill my romance.

During all Act 2, I have Isobel as a quest target.

I am doing something wrong? What's wrong?

Thanks.